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Who enjoys solitude? autonomous functioning (but not introversion) predicts self-determined motivation (but not preference) for solitude

Autonomous functioning predicts self-determined motivation for solitude

https://orcid.org/0000-0003-0777-4204

Nguyen

Thuy-vy T.

Conceptualization Data curation Formal analysis Methodology Writing – original draft ¹ * Weinstein

Netta

Supervision Writing – original draft Writing – review & editing ² Ryan

Richard M.

Writing – review & editing ³

Durham University, Durham, United Kingdom

University of Reading, Reading, United Kingdom

Australian Catholic University, North Sydney, Australia

Brown

Kirk Warren

Editor

Virginia Commonwealth University, UNITED STATES

The authors have declared that no competing interests exist.

* E-mail: vy.nguyen@durham.ac.uk.

25 5 2022

2022

17 5

e0267185

26 3 2021 4 4 2022

2022

Nguyen et al

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Within the solitude literature, two discrete constructs reflect different perspectives on how time spent alone is motivated. Self-determined motivation for solitude reflects wanting time alone to find enjoyment and gain meaningful benefits from it, whereas preference for solitude concerns wanting time for oneself over others’ company regardless of reasons for why time alone is wanted. We investigated two personality characteristics: introversion from Big-Five personality theory and dispositional autonomy from self-determination theory. In two diary studies university students completed personality measures and reported about their experiences with time spent alone over a period of seven days. Across both studies, contrary to popular belief that introverts spend time alone because they enjoy it, results showed no evidence that introversion is predictive of either preference or motivation for solitude. Dispositional autonomy–the tendency to regulate from a place of self-congruence, interest, and lack of pressure–consistently predicted self-determined motivation for solitude but was unrelated to preference for solitude. These findings provided evidence supporting the link between valuing time spent alone with individual differences in the capacity to self-regulate in choiceful and authentic way.

The author(s) received no specific funding for this work.

Data Availability

All relevant data are within the paper.

Introduction

There has been a growing interest in understanding why people spend time alone [1–4]. This topic is interesting in no small part because pursuits for time alone have been rendered incompatible with our human nature as social organisms [5]. Yet despite the sociality of people, there are times when people seek time alone because they see it as enjoyable, worthwhile, and valuable. Being motivated to spend time alone for those reasons has been referred to as having self-determined motivation for solitude [1, 2, 6]–a concept that stems from the self-determination theory (SDT) literature [7, 8], suggesting that motivation for solitude may be personally endorsed and intrinsically motivated. Evidence is mounting that self-determined motivation for solitude is empirically distinct from merely preferring solitude over social time [1, 9, 10], but there is little knowledge about what drives people to self-determined motivation for solitude, even when they do not necessarily prefer to be alone. In this paper, we explore the role that personality plays in both motivation and preference for solitude, focusing on two personality characteristics that should predict the two constructs differentially: autonomous orientation, which is likely to drive self-determined motivation, and introversion, likely to drive preference.

Self-determined motivation for solitude

While the benefits of solitude are not new discoveries, it is still common to assume that people dislike being alone and rarely seek it out. Only recently, researchers begin to study different qualities of motivation for solitude and recognize that people do seek out solitude for self-determined reasons. From the SDT perspective, having high self-determined motivation for being alone represents choosing to spend time alone because solitude offers enjoyment or offers some personal benefits. Researchers who have studied this concept [1, 2, 6] contrasted self-determined motivation for spending time alone with motivations that are rooted in feeling like one is forced or coerced into aloneness through other individuals or external circumstance (not self-determined solitude). For example, a person with self-determined motivation to spend time alone will take time out of their day to embrace the benefits that solitude brings, such as opportunities for relaxation, creativity or freedom.

The distinction between choosing solitude because it is valued and feeling forced to be alone are apparent in both methods of measuring self-determined and not self-determined motivation for solitude from the self-determination theory perspective. One operationalization is through the Motivation for Solitude Scale (MSS-SF) [1], which includes items that pertain to reasons for spending time alone for positive and constructive benefits (e.g., creativity, relaxation, self-discovery) and those that concern reasons for being alone due to not feeling oneself or accepted around other people. The MSS-SF specified different positive and negative reasons for approaching solitude. The other, adapted from the Self-Regulation Questionnaire by Ryan and Connell [11], directly asks whether the reasons for spending time alone have to do with finding it enjoyable or valuable, and also asks whether participants are alone because of their internal compulsion (i.e., feeling like one should be alone) or some external circumstances (i.e., being made to be alone). The latter measure phrases items more broadly so they can be used in laboratory settings or daily assessments where participants may not have specific reasons for why they would like to be alone at that moment or on a specific day.

Both scales have been used to demonstrate that self-determined motivation correlates with positive functioning in general [1], as well as with more proximal outcomes [2]. These positive reasons for spending time alone have been documented in studies not only from Western samples [1, 12], but also in one East Asian sample [13].

Distinction between preference for solitude and self-determined motivation for solitude

From an SDT perspective, self-determined motivation does not concern with people’s behaving in ways that are in line with their preference [14]. In other words, when a person prefers a course of action, this preference might be based on available options rather than reflecting personal interests or values. As such, in relation to spending time alone, self-determined motivation for solitude ought to be differentiated from the preference that someone might have at any given time when they decide between two available options: being alone versus being with others. Preference for solitude is a concept rooted in the social approach and social avoidance motivation literature. Within this perspective, preference for solitude represents a motivation to move away from social interactions to avoid undesired interactional outcomes, and has been reported in young children [4, 15] and adolescents [16–18]. Among adults, preference for solitude has been showed to be associated with trait loneliness [19] and previous experiences of ostracism [20].

Originally, preference for solitude has been studied as a form of social withdrawal in young children. However, it was stressed that, different from other well-studied forms of social withdrawal, preference for solitude is not underlined by shyness or social anxiety [4, 21]. Such discovery gave rise to a new phenomenon referred to as unsociability [4]–a term used to characterize some children’s tendency to spend time or play alone, whose behavior is not driven by social difficulties or unpleasant interactions with peers. Other researchers have described adults who display similar patterns of behaviors as those who have high preference for solitude [17, 20] or possess a solitropic orientation [22]. Although these different terms have been used to describe the propensity toward spending time alone over interacting with others (e.g., unsociability, preference for solitude, solitropic orientation), in this paper we will generally refer to this phenomenon as preference for solitude.

To summarize, the two literatures identify disparate outcomes when one is seeking solitude. Self-determined motivation has been consistently operationalized as a form of a healthy and adaptive motivation for spending time alone [1, 6, 9] that yields positive associations with well-being correlates. On the other hand, the way that preference for solitude has been operationalized has led to its associations with maladaptive constructs like loneliness [1, 19, 23] and social anxiety [1]. More importantly, while the literature clearly demonstrated that these two concepts are independent of one another, the correlations between measures of self-determined motivation for solitude and preference for solitude have been inconsistent. Burger’s 12-item measure of preference for solitude [19] showed positive correlations with measures that Thomas and Azmitia [1] used to assess both self-determined and not-self-determined motivation for solitude in late adolescence. Another study that examined preference for solitude in adults older than 35 years of age showed a positive correlation between Burger’s preference for solitude scale and self-determined motivation for solitude, and also a negative correlation between preference and not self-determined motivation for solitude [10]. These correlations suggest that, for those beyond adolescence and young adulthood, preference for solitude is associated more with self-determined rather than not-self-determined motivation for solitude, whereas preference for solitude in late adolescence could reflect both types of motivation.

In this paper, we explore two key personality predictors that may help to explain how both motivation and preference are shaped through the relationship that people have towards solitude, or time spent with themselves. We approach the question of what sets motivation and preference apart from the view that stable dispositions can predispose individuals to a type of relationship with solitude; for example, one characterized by self-determined motivation, or another kind, for example one that is predominantly characterized by preference.

Dispositional autonomy as predictor of self-determined motivation for solitude

Identifying dispositional characteristics that may predict daily self-determined motivation for solitude can be informed by the developmental psychology literature. First, it is important to highlight that solitude is not inherently comfortable, and developmental psychologists suggest that a healthy attitude toward solitude, despite the challenges of being alone as social animals, signals positive development and emotional maturity [24–26]. Particularly, the prominent developmental psychoanalyst Donald Winnicott, asserted that the capacity to be alone is an ability that develops from a nurturing environment where children are allowed opportunities to express their freedom through play without intrusion from caregivers. Indeed, this view of healthy motivation for solitude has been reflected in recent empirical works, which showed that the pursuit of solitude for its benefits to creativity and relaxation was linked to experiences of personal growth in young adults [1]. When individuals experience positive solitude, they often attribute this to the freedom to engage in chosen activities and the removal of social pressure and surveillance [12]. From these literatures, our research was aimed at testing the hypothesis that solitude allows opportunities for autonomous self-expression–being able to engage in activities that reflect one’s interests and choices. To test this hypothesis, one concept in social-personality psychology that captures the propensity for autonomous self-expression is dispositional autonomy.

Dispositional autonomy refers to the degree to which an individual tends to regulate their behaviors in a more or less autonomous, or choiceful, manner–that is, endorsed by the self and motivated through interest or valuing [27]. Building on early SDT theorizing [28], dispositional autonomy is comprised of three components that together make up the concept: 1) a tendency toward self-congruence, 2) an ability to take interest in one’s emotional experiences, and 3) a lower vulnerability to momentary pressures and controls [27]. Findings show that individuals with this disposition experience daily activities more positively, and better integrate life experiences into their other views of the self with less internal conflict [29]. Further, dispositional autonomy seems important for felt comfort with one’s experiences of the self [30], and for making sense of potentially conflictual emotions [31].

Previous literature has demonstrated that those who behave in ways that are consistent with their beliefs and values tend to be motivated by intrinsic and self-determined reasons in whatever they do [29, 30, 32]. However, it is important to highlight that this might not be true for solitude, which is commonly portrayed as a challenging experience for people. This is particularly relevant for young adults because they find solitude more difficult than older age groups [33, 34] unless they have been allowed opportunities to develop a capacity to enjoy it. Given this, an investigation of dispositional autonomy that represents that capacity speaks to Winnicott’s theorizing [25] discussed above, which has not been considered in previous studies. As such, while no empirical findings have linked dispositional autonomy to solitary experiences, we considered dispositional autonomy as an important predictor of the capacity to be alone because of a healthy and non-defensive relationship with oneself [34]. We expected that, because individuals high in dispositional autonomy would be likely to enjoy their inner world as much as other people’s company, dispositional autonomy would yield no significant association with preference for solitude over social interactions. Nonetheless, dispositional autonomy would relate more to the enjoyment of solitude for its own sake; that is, a person who is high in dispositional autonomy would show higher levels of self-determined motivation for solitude.

Introversion as a predictor of preference for solitude

More widely studied than dispositional autonomy, when it comes to predicting who likes spending time alone, laypersons and researchers alike intuit that introversion must play an important role. An introvert is someone who is reserved and inhibited, so it is reasonable that they would prefer being alone to being in social interactions [e.g., 35–37]. It has been showed that individual difference in preference for solitude correlate positively with introversion [19]. Another study by Leary, Herbst, and McCrary [22] that collected data from a variety of different personality measures showed that several traits related to the introversion-extraversion dimension of personality, such as sociability, extraversion as measured by the Big-Five inventory, need to belong, and desire for social contact, correlated negatively with how frequently participants reported engaging in solitary activities. Similar patterns of findings were also shown in relation to the likelihood of people reporting they would do certain activities alone. The authors also found that these characteristics that pertain to being a sociable, extraverted, and people-oriented person also correlated with deriving less enjoyment from engaging in activities alone. These findings were taken to mean that those who lack those qualities of being sociable, extraverted, and people-oriented should prefer more aloneness and enjoy it more.

However, while Burger [19] and Leary et al. [22] used one-time measures of people’s evaluations of their own personality and attitudes toward solitude, a study by Srivastava et al. [38], which used a day-construction design and collected data from participants’ day-to-day experiences, showed a different pattern. When asked to report levels of positive affect while interacting with other people and while not interacting, those high in extraversion reported feeling more positive in relation to both types of experiences. Interestingly, those low in extraversion also felt more positive in social interaction than when not interacting, and in fact felt less positive than extraverts when not interacting with others. This presents an interesting picture for introverts when it comes to their time spent alone; they generally show a greater preference for solitude than extraverts [1], because they do not derive as much benefit out of social interactions as do extraverts, but they might not necessarily enjoy time alone more [39]. In other words, introverts’ preference for solitude might be driven more by the lack of appeal held by available social experiences, and less by their anticipation that spending time alone would be enjoyable. As such, and consistent with the recent findings by Thomas and Azmitia [1], we predicted that scores on introversion would positively relate to ratings of daily preference for solitude. In this research, we operationalized introversion as having the opposite qualities to those that are associated with extraversion; that is, introverts tend to be more reserved, quieter, less talkative, energetic, and assertive. We will describe how we assess introversion in the method section. On the other hand, we did not expect that introversion would positively relate with self-determined motivation for solitude because someone who possesses those qualities described below might prefer to have more time for themselves, but they might do so for either self-determined or not self-determined reasons.

The present research

This research was conducted to differentiate preference for solitude and self-determined motivation for solitude through understanding their different links to personality characteristics. Informed by theorizing and extant research discussed above, we predicted that introversion would only relate to preference for solitude but not necessarily to self-determined motivation for solitude. On the other hands, we predicted dispositional autonomy–the capacity to self-regulate in an autonomous and volitional way—would relate to self-determined motivation for solitude but not to preference for solitude. Thus, the present empirical tests served to establish discriminant validity of the two constructs by investigating their personality underpinnings.

To do so we conducted two daily diary studies. The advantage of this design is that it allows us to capture how personality characteristics relate to solitary experience on a daily basis, an advance compared to previous methodologies that relied on retrospective self-reports collected at one time of people’s experiences with being alone. This approach also had some advantages relative to lab experiments on solitude [2] in that it allowed a window into experiences as they naturally occur in people’s’ daily lives. Specifically, we tested two confirmatory hypotheses:

Dispositional autonomy would show positive association with self-determined motivation for solitude. We did not predict that dispositional autonomy would correlate with preference for solitude.

Introversion would show positive association with preference for solitude. We did not predict that introversion would correlate with self-determined motivation for solitude.

Study 1 Study 1 method Participants

One hundred and eighty-three undergraduate students (153 women) between the age of 18 and 28 years (M_age = 20 years, SD = 1.36) participated in the study, after excluding five who signed up but either did not complete the initial survey (three participants) or did not participate in the diary portion of the study (two participants). Sample sizes were not determined based on power analyses. Rather, we determined sample size based on a realistic expectation of how many participants we could recruit from the pool that was available. We selected to test study hypotheses with students because we could access and track this population, and because there was no external funding available to recruit community participants outside of undergraduate participant pool.

However, it is worth noting that this age group of emerging adults has been the focus of past research that has shown consistent links between self-determined motivation and well-being in solitude [1, 2], adding value to our current tests of antecedents of self-determined motivation. The final sample provided 1227 units (in days) of data. The sample consisted of 53% Whites and Caucasian participants, 35% Asians or Pacific Islander participants, 5% Black or African American participants, and 7% participants of other races or multi-races. Eighty percent of participants completed all seven days of diary, 14% completed 6 days, 3% completed 5 days, less than 2% completed 4 days and less than 2% completed 3 days.

Procedure

Two-hundred time slots were posted for a duration of one week. Participants were instructed they would complete an initial survey to enroll into the email list, and that they will receive daily surveys starting on Monday of the following week. In all, participants were provided with eight surveys: One initial survey that assessed their personality, and seven daily diary surveys. Prior to the diary surveys, participants completed a questionnaire that included questions about their personality. Subsequently, daily surveys were sent by email after 5PM each day and these surveys were set to expire at 6AM the next day to prevent delayed responding. Each survey took approximately 20 to 30 minutes to complete. Each survey completed was incentivized with extra course credit, and those who completed all eight surveys were enrolled into a lottery drawing for a $25 gift card.

Initial survey. All participants were enrolled after submitting an initial survey. Included in the initial survey were several personality measures, including the Introversion subscale from the Big-Five Inventory [40] and the Index of Autonomous Functioning (IAF) [27]. Descriptions of personality measures used in this study are provided below.

Dispositional autonomy. Dispositional autonomy was measured with the 15-item Index of Autonomous Functioning [27]. This measure captures three aspects of an autonomous disposition, namely, a tendency to act in congruence with one’s values and beliefs, a reliance to being susceptible external controls and pressures, and a tendency to take an interest in one’s internal feelings and experiences. Participants rated their responses on a 5-point Likert-scale, ranging from 1 = “Strongly disagree” to 5 = “Strongly agree”. Items include “My decisions represent my most important values and feelings”, “I do things in order to avoid feeling ashamed”, and “I am deeply curious when I react with fear and anxiety”. All fifteen items were averaged after items from the susceptibility to pressure subscale were reversed, as recommended by Weinstein et al. [27]. Overall scale reliability was acceptable (α = .78).

Introversion. To measure introversion, we used the eight items from John and Srivastava’s [40] Big-Five Inventory (BFI) that were used to measure the Big-Five trait of extraversion. This measure includes descriptive statements of how extraverts often behave, such as being “talkative” and “full of energy”. We used this instead of the NEO-PI (Neuroticism, Extraversion, Openness Personality Inventory [41]) because the NEO-PI includes positive emotions and warmth as descriptors of extraversion, which could potentially portray introversion as lacking those positive qualities (see comparison between NEO-PI and BFI in Zillig et al [42]). Using the BFI Extraversion subscale, we showed participants a stem stating, “I see myself as someone who…”, and they proceeded to rate their agreement to a series of descriptive statements. We reverse-coded the extraversion-related items like “talkative” and “full of energy”, and averaged them with items included “reserved” and “quiet”, such that higher overall scores reflected introversion (α = .87). Participants rated their responses on a 5-point Likert scale, ranging from 1 = “strongly disagree” to 5 = “strongly agree”.

Diary survey. Each day, participants received an email with links to diary surveys that are made available every day at 5PM and expired at 6AM. Participants were instructed to complete the survey at any times between this interval that were convenient to them. For each diary survey, participants were asked about a significant event that happened to them that day, their experiences of such event (e.g., autonomy, need satisfaction, positive and negative affect), their self-determined motivation for solitude and levels of preference for solitude. Only self-determined motivation for solitude and preference for solitude were the variables of interest for this present paper, whereas other questions were part of a separate project studying the link between daily positive events and later memories of such events. Because our survey could not capture momentary experiences with solitude (an experience sampling design would be more appropriate), we did not ask participants about any specific solitary experiences but only asked about their general evaluations of their daily experiences with it.

Self-determined motivation for solitude. For this variable, we used the scale from Nguyen et al. [2], which we felt was more appropriate for a diary study design because it measures state-level motivation for solitude and could better capture day-to-day fluctuation. In comparison, the measure developed by Thomas and Azmitia [1] is more appropriate for distinguishing individual differences in self-determined motivation for solitude. For our measure, respondents were presented with a prompt: “Different people spend time by themselves for different reasons. Please indicate the extent to which each of the following reasons applies to you regarding all the instances when you were by yourself today”. Four items assessed self-determined motivation for solitude, namely the reasons for spending time alone because of the value in, and enjoyment of, the activity. Respondents indicated their agreement on scales from 1 (not at all true) to 7 (very true). Those items were: “I simply was enjoying my time alone for its own sake”, “I was alone because having time to myself is an important part of my day”, “I was alone because solitude is one of the things I value in my life”, and “I found it enjoyable to be in my own company”. Items (α = .91) yielded high reliability across all items and assessments. Therefore, we averaged all items for a total score reflecting higher self-determined motivation for solitude reported on each of the seven days.

Preference for solitude. We adapted items from a measure by Wang et al. [18], which assessed preference for solitude—the degree to which participants desired to be alone more than with others. We decided to use this measure rather than Burger’s preference for solitude [19] because Wang et al.’s measure is shorter and thus less burdensome to participants who complete it repeatedly throughout the daily diary procedure. Further, Burger’s measure includes certain items that describe specific situations which might not apply to participants’ daily experiences, such as “I like to vacation in places where there are few people around and a lot of serenity and quiet” or “If I were to take a several-hour plane trip, I would like to sit next to someone who was pleasant to talk with”. Some of Burger’s items also conflate preference and desire to be alone with enjoyment and benefits of being alone (i.e., “I enjoy being by myself”, Time spent alone is often productive for me”). Because we aimed to distinguish preference and desire from motivation to be alone for the enjoyment and benefits of solitude, we opted not to include those items in our measure. Instead, the items we used were “Today I wanted to be by myself rather than with others”, “Today, I would prefer being with other people than being by myself” (reverse coded), and “Today, I had a strong desire to get away from others to be by myself”. We modified Wang et al.’s original measure, which they used for children between 8^th and 12^th grades, so that the items are more appropriate for the ages of our sample. Participants indicated their agreement on scales from 1 (not at all true) to 7 (very true). These items were averaged to create a composite score for daily preference for solitude. Items yielded high reliability across all items and assessments (α = .99).

Ethics statement. Both studies were reviewed and approved by the Research Subjects Review Board at the University of Rochester (Study 1: RSRB00070882; Study 2: RSRB3612) before the studies began. For both studies, participants were provided an information letter hosted online. The participants were asked to confirm their consent to participation by clicking a “Next” button to proceed to the initial survey to report their demographic information and fill out personality questionnaire. The information letter specifically instructed the participants that they can skip any of the questions that they did not want to answer or withdraw their participation at any time without penalty. The same consent form was presented in all phases of the study.

Analytic strategy. Random-intercept models were conducted using the ‘lme4’ package in R program using full maximum likelihood for parameter estimations of both fixed and random effects. All data and code are shared on OSF (link: https://osf.io/yfgnm/?view_only=fcb98c41581c49ef9c2fd8c6765d6467).

Study 1 results Scale reliability

Analyses of reliability for preference for solitude items revealed small proportion of variance explained by between-person differences while there was more person-by-day variation, suggesting that preference for solitude varies differently on a day-to-day basis depending on individuals. On the other hand, we observed large proportion of variance explained by between-person differences for self-determined motivation for solitude, suggesting that we had some participants that were higher or lower in general on this variable across all days and all items. We also observed person-by-day variation, meaning daily variation on this measure differed across individuals as well. Nonetheless, for both measures, there was not much variance at the day-by-item or person-by-item levels, suggesting that we had high reliability for items across days and across participants (.99 for preference and .91 for self-determined motivation) and items could be combined in composites for each day.

Confirmatory analyses

The daily average for self-determined motivation for solitude was M = 4.37 (Median = 4.5, SD = 1.81), and for preference for solitude was M = 3.51 (Median = 3.33, SD = 1.59). Both introversion and dispositional autonomy were entered simultaneously into the random-intercept regression models, one defining preference for solitude as outcome and the other defining self-determined motivation for solitude as the outcome. Both models satisfied normality assumption and revealed an ICC of .56 for self-determined motivation and .23 for preference for solitude.

Self-determined motivation for solitude. In the model predicting self-determined motivation for solitude (Table 1), results indicated a positive association between dispositional autonomy and self-determined motivation for solitude (ß = .14, CI 95% = [.03, .26], t(1221) = 2.40, p = .016). Controlling for gender and ethnicity revealed similar results (ß = .18, CI 95% = [.06, .29], t(1221) = 2.92, p = .004). Therefore, our second hypothesis was supported. We did not find significant association between introversion and self-determined motivation for solitude (ß = .07, CI 95% = [-.04, .19], t(1221) = 1.23, p = .220).

10.1371/journal.pone.0267185.t001

Table 1 Random-intercept models that include introversion and dispositional autonomy predicting daily self-determined motivation for solitude (Study 1).

	Self-determined motivation						Self-determined motivation (controlling for gender & ethnicity)
Predictors	B	CI(B)	ß	CI(ß)	t	p	B	CI(B)	ß	CI(ß)	t	p
(Intercept)	2.05	[.16, 3.94]	.00	[-.11, .12]	2.13	.034	1.02	[-1.01, 3.04]	-.31	[-.65, .04]	.99	.325
Introversion	.14	[-.11, .39]	.07	[-.05, .18]	1.11	.266	.15	[-.09, .40]	.07	[-.04, .19]	1.23	.220
Dispositional autonomy	.53	[.10, .97]	.14	[.03, .26]	2.40	.016	.65	[.21, 1.09]	.18	[.06, .29]	2.92	.004
Gender [woman vs. others]							.37	[-.16, .90]	.20	[-.09, .50]	1.35	.176
Ethnicity [Asian vs. others]							.64	[.04, 1.24]	.35	[.02, .69]	2.10	.036
Ethnicity [White vs. others]							.10	[-.46, .66]	.06	[-.25, .37]	0.35	.724
Reliability estimates and estimates of between-person reliability and reliability of change
	Variance	Percent
σ²_Person	1.76	.47
σ²_Day	-0.01	.00
σ²_Item	0.03	.01
σ²_{Person x Day}	1.26	.33
σ²_{Person x Item}	0.10	.03
σ²_{Day x Item}	0.01	.00
σ²_Error	0.62	.16

Preference for solitude. Results (Table 2) did not show a significant association between introversion and preference for solitude (ß = .03, CI 95% = [-.06, .12], t(1221) = 0.72, p = 0.470). Therefore, our first hypothesis was not supported. We also did not find significant association between dispositional autonomy and preference for solitude (ß = -.01, CI 95% = [-.10, .08], t(1221) = -0.23, p = 0.821). Controlling for gender and ethnicity did not change the results of this model.

10.1371/journal.pone.0267185.t002

Table 2 Random-intercept models that include introversion and dispositional autonomy predicting daily preference for solitude (Study 1).

	Preference for solitude							Preference for solitude (controlling for gender & ethnicity)
Predictors	B	CI(B)		ß	CI(ß)	t	p	B	CI(B)	ß	CI(ß)	t	p
(Intercept)	3.46	[2.20, 4.72]		.00	[-.08, .09]	5.40	< .001	2.98	[1.61, 4.35]	-.18	[-.44, .08]	4.28	< .001
Introversion	.06	[-.10, .23]		.03	[-.06, .12]	0.72	.470	.07	[-.09, .24]	.04	[-.05, .13]	0.88	.379
Dispositional autonomy	-.03	[-.32, .26]		-.01	[-.10, .08]	-0.23	.821	.01	[-.29, .31]	.00	[-.09, .09]	0.07	.945
Gender [woman vs. others]								.18	[-.18, .54]	.11	[-.11, .34]	0.99	.323
Ethnicity [Asian vs. others]								.27	[-.14, .67]	.17	[-.09, .42]	1.30	.194
Ethnicity [White vs. others]								.10	[-.28, .48]	.06	[-.17, .30]	0.52	.606
Reliability estimates and estimates of between-person reliability and reliability of change
	Variance		Percent
σ²_Person	0.44		.11
σ²_Day	0.05		.01
σ²_Item	0.25		.07
σ²_{Person x Day}	1.46		0.38
σ²_{Person x Item}	0.39		.10
σ²_{Day x Item}	0.00		.00
σ²_Error	1.23		.32

Study 2

In Study 1, we found that dispositional autonomy predicted greater self-determined motivation for solitude. We did not find evidence for the expected association between introversion and preference for solitude. It is important to note that preference for solitude in Study 1 appeared to vary highly on a day-to-day basis within individuals, suggesting that variation in preference for solitude might be less a function of individual differences and more a function of experiences within the day. However, this finding could have resulted from a lack of between-person variation in this particular sample, so we recruited a larger sample in Study 2 and tested the same hypotheses again. Additionally, because we only compared predictive ability of dispositional autonomy to introversion, we couldn’t draw a conclusion on whether dispositional autonomy represents a unique individual difference that predicted self-determined motivation for solitude above and beyond the other Big-Five traits. Particularly, dispositional autonomy shared some variance and positive correlations with openness to experience, agreeableness, and conscientiousness dimensions of Big-Five personality [43]. A meta-analysis of experience-sampling studies also showed that all Big-Five traits explained significantly individuals’ daily state-level experiences and behaviors [44]. So, there is a case to be made about the ability of dispositional autonomy to predict self-determined motivation for solitude above and beyond Big-Five personality traits. As such, in Study 2, the same design was adopted with two improvements: 1) We used a larger sample size, and 2) We included all Big-Five traits to our mixed-effect models.

Study 2 method Participants

Three hundred sign-ups were made available to undergraduate students, and 287 participants between 18 and 28 years of age (186 women, 99 men, 1 unspecified) completed the initial survey. Similar to Study 1, sample size was not determined by power analysis but based on realistic expectation of how many participants we can recruit from the available pool. The sample was predominantly White (43%) and Asian (42%) participants, while Black participants made up 9% and Hispanic or Latino participants made up approximately 10% of the sample.

Procedure

When participants signed up, they were asked to complete a questionnaire consisting of the dispositional autonomy (α = .76) and Big-Five introversion (α = .87) scales. Study 2’s design was the same as Study 1, except for the addition of all other Big-Five traits. Specifically, this time we evaluated the extent to which introversion and dispositional autonomy each predicted solitude-relevant outcomes above and beyond agreeableness (α = .79), conscientiousness (α = .78), neuroticism (α = .81), and openness to experience (α = .72). All Big-Five traits, including the subscale used in Study 1 to measure introversion, were assessed using the Big-Five Inventory (40). Again, participants were presented with a stem: “I see myself as someone who…”. Agreeableness was measured with items such as “is helpful and unselfish with others”. Conscientiousness was measured with items such as “does a thorough job”. Neuroticism was measured with items such as “worries a lot”. Openness to experience was measured with items such as “values artistic, aesthetic experiences”. All items are included in codebooks shared on our OSF folder.

After participants filled out the initial questionnaire, on Monday of the week following signing up, participants completed daily surveys for five days until Friday. For the diary surveys, participants reported their preference for solitude (α = .89) and self-determined motivation for solitude (α = .97) on that day. Participants also reported on other experiences such as their social media usage and the extent to which they experienced their social interactions and alone time as being authentic or inauthentic; those data were collected for another project. Only the data on preference for solitude and self-determined motivation for solitude are described here. Sixteen participants who filled out the initial survey did not the diary portion of the study and one participant had missing values on the personality data; those were dropped from the data set. The final sample has 270 participants who provided a total of 1150 units (in days) of data.

Analytic strategy. Similar to Study 1, we conducted two separate random-effects regression models using maximal likelihood estimations. The models included Big-Five personality traits and dispositional autonomy as simultaneous predictors on preference for solitude and self-determined motivation for solitude.

Study 2 results Scale reliability

Once again, we observed that preference for solitude appears to vary on a day-to-day basis compared to self-determined motivation for solitude, and that the larger percentage of variance in self-determined motivation for solitude could be accounted for by individual differences (see variance components in Tables 3 and 4). Nonetheless, for both measures, there was not much variance at the day-by-item or person-by-item levels, suggesting that we had high reliability for items across days and across participants (.89 for preference and .97 for self-determined motivation) and items could be combined in composites for each day within each participant.

10.1371/journal.pone.0267185.t003

Table 3 Random-intercept models that include introversion, dispositional autonomy, and all other big-five traits, predicting daily self-determined motivation for solitude (Study 2).

	Self-determined motivation						Self-determined motivation (controlling for gender & ethnicity)
Predictors	B	CI(B)	ß	CI(ß)	t	p	B	CI(B)	ß	CI(ß)	t	p
(Intercept)	2.04	[.08, 4.00]	.01	[-.08, .09]	2.05	.041	2.51	[.48, 4.54]	-.14	[-.36, .07]	2.43	.015
Agreeableness	-.25	[-.52, .02]	-.09	[-.19, .01]	-1.79	.074	-.26	[-.53, .00]	-.10	[-.20, .00]	-1.94	.053
Neuroticism	-.10	[-.32, .12]	-.04	[-.14, .05]	-0.87	.382	-.19	[-.42, .05]	-.08	[-.19, .02]	-1.56	.119
Openness to experience	.21	[-.08, .51]	.07	[-.03, .17]	1.43	.154	.18	[-.11, .47]	.06	[-.04, .16]	1.24	.214
Conscientiousness	.27	[.00, .54]	.10	[.00, .20]	2.00	.046	.24	[-.03, .52]	.09	[-.01, .19]	1.77	.077
Introversion	.21	[.02, .40]	.10	[.01, .20]	2.14	.033	.19	[-.00, .38]	.09	[-.00, .19]	1.95	.052
Dispositional autonomy	.38	[.00, .76]	.11	[.00, .21]	1.97	.049	.35	[-.03, .73]	.10	[-.01, .21]	1.81	.071
Gender [woman vs. others]							.42	[.09, .75]	.26	[.06, .46]	2.50	.013
Ethnicity [Asian vs. others]							.03	[-.35, .41]	.02	[-.21, .25]	0.17	.865
Ethnicity [White vs. others]							-.12	[-.50, .26]	-.07	[-.31, .16]	-0.62	.532
Reliability estimates and estimates of between-person reliability and reliability of change
	Variance	Percent
σ²_Person	1.02	.33
σ²_Day	0.01	.00
σ²_Item	0.02				.01
σ²_{Person x Day}	1.21	.39
σ²_{Person x Item}	0.08	.02
σ²_{Day x Item}	0.00	.00
σ²_Error	0.73	.24

10.1371/journal.pone.0267185.t004

Table 4 Random-intercept models that include introversion, dispositional autonomy, and all other big-five traits, predicting daily preference for solitude (Study 2).

	Preference for solitude						Preference for solitude (controlling for gender & ethnicity)
Predictors	B	CI(B)	ß	CI(ß)	t	p	B	CI(B)	ß	CI(ß)	t	p
(Intercept)	4.46	[2.96, 5.96]	.00	[-.08, .08]	5.82	< .001	4.75	[3.19, 6.31]	-.05	[-.24, .15]	5.97	< .001
Agreeableness	-.42	[-.62, -.21]	-.18	[-.27, -.09]	-3.96	< .001	-.42	[-.63, -.22]	-.19	[-.28, -.10]	-4.03	< .001
Neuroticism	-.11	[-.28, .06]	-.06	[-.14, .03]	-1.28	.201	-.15	[-.33, .03]	-.08	[-.17, .02]	-1.64	.100
Openness to experience	.05	[-.17, .28]	.02	[-.07, .11]	0.46	.647	.17	[-.04, .38]	.07	[-.02, .16]	1.56	.119
Conscientiousness	.17	[-.03, .38]	.08	[-.01, .17]	1.67	.095	.12	[-.03, .26]	.07	[-.02, .15]	1.57	.116
Introversion	.13	[-.02, .28]	.08	[-.01, .16]	1.74	.083	.01	[-.28, .30]	.00	[-.09, .10]	0.08	.937
Dispositional autonomy	.04	[-.25, .33]	.01	[-.08, .11]	0.24	.807	.04	[-.19, .26]	.01	[-.08, .10]	0.31	.758
Gender [woman vs. others]							.24	[-.01, .50]	.18	[-.01, .36]	1.88	.061
Ethnicity [Asian vs. others]							-.05	[-.35, .24]	-.04	[-.25, .17]	-.37	.713
Ethnicity [White vs. others]							-.18	[-.48, .11]	-.13	[-.34, .08]	-1.21	.228
Reliability estimates and estimates of between-person reliability and reliability of change
	Variance	Percent
σ²_Person	0.43	.13
σ²_Day	0.01	.00
σ²_Item	0.31	.09
σ²_{Person x Day}	0.99	.29
σ²_{Person x Item}	0.33	.10
σ²_{Day x Item}	0.01	.00
σ²_Error	1.30	.38

Confirmatory analyses

The daily average for self-determined motivation for solitude was M = 4.43 (Median = 4.5, SD = 1.63) and for preference for solitude was M = 3.85 (Median = 4, SD = 1.39). Both introversion and dispositional autonomy, and all other Big-Five traits, were entered simultaneously into the random-intercept regression models, one defining preference for solitude as outcome and the other defining self-determined motivation for solitude as the outcome. Both models satisfied normality assumption and revealed an ICC of .44 for self-determined motivation and .29 for preference for solitude.

The model predicting self-determined motivation for solitude showed that dispositional autonomy was a significant predictor (β = .11, CI 95% = [.00, .21], t(1140) = 1.97, p = .049). Additionally, introversion yielded significant positive association in this model (β = .10, CI 95% = [.01, .20], t(1140) = 2.14, p = .033), and conscientiousness also yielded significant positive association with self-determined motivation for solitude (β = .10, CI 95% = [.00, .54], t(1140) = 2.00, p = .046), but other Big-Five traits did not (see Table 3). However, once gender and ethnicity were controlled for in the model, all three predictors, including dispositional autonomy, introversion, and conscientiousness, no longer predicted self-determined motivation for solitude. In this latter model with covariates, being a woman was associated on average with greater self-determined motivation for solitude (β = .26, CI 95% = [.06, .46], t(1137) = 2.50, p = .013).

The models (Table 4) predicting preference for solitude did not show evidence of significant association between introversion and preference for solitude (β = .080, CI 95% = [-.01, .16], t(1141) = 1.74, p = .083). Again, in Study 2, with a larger sample size, our hypothesis was not supported. However, we found that agreeableness emerged as a significant predictor of preference for solitude, and the association was in the negative direction (β = -.18, CI 95% = [-.27, -.09], t(1141) = -3.96, p < .001). This suggested that those who have a friendly and warm personality might be less likely to prefer spending time alone. The results remained similar when we controlled for gender and ethnicity (see Table 4).

General discussion

In two daily diary studies we examined how personality characteristics are linked to individuals’ motivation and preference for solitude. This research distinguished between two phenomena in the solitude literature: First, daily self-determined motivation for solitude refers to the motivation for time alone in order to find enjoyment and gain meaningful benefits from it, and second, daily preference for solitude refers to favoring being alone rather than being with other people. We proposed that these two phenomena are conceptually distinct and therefore could be associated with different personality traits. Specifically, we argued that self-determined motivation–pursuing solitude because of the value, enjoyment, and personal importance of it, requires a comfort with and even propensity towards self-regulation and therefore should be predicted by autonomous functioning. On the other hand, no such self-regulation was necessary in order to merely want to be alone more so than spending time with other people.

Our hypotheses were driven by the previous literature suggesting that preference for solitude was generally associated with traits related to disfavoring social interactions due to either previous negative experience (i.e., history of social exclusion [16, 34]) or experiencing low belongingness to one’s social groups (i.e., loneliness [15, 18]). As such, we expected that individuals who were high on introversion would be disposed to preferring solitude in their daily lives. On the other hand, while there has not been much research directly investigating personality correlates of self-determined motivation for solitude, previous research suggests that it signifies positive development in emerging adults [1], and better regulatory capacity in adults [2]. We therefore expected that individuals higher in dispositional autonomy would be more disposed to daily self-determined motivation for solitude in their daily lives.

Dispositional autonomy was made up of three components that are thought to move individuals closer to their selves and promote self-driven functioning, including the propensity to behave in accordance to one’s belief and values, the ability to not be carried away by social influences and internal negativity, and the tendency to engage in “reflective self-understanding” [27]. That is, the construct assumes that these qualities reflect a general self-regulatory capacity to experience one’s actions and behaviors as self-organized or self-initiated [45].

Across both daily diary studies, we found convergent evidence that dispositional autonomy related to more self-determined motivation for solitude. The associations between dispositional autonomy and self-determined motivation for solitude were consistently positive across the two studies. There were four models conducted across studies. In Study 1, we tested two models with the first one including only introversion and dispositional autonomy and the second one controlling for gender and ethnicity. In Study 2 we tested two models with the first one including introversion, dispositional autonomy, and other four Big-Five traits, and the second one controlling for gender and ethnicity. Out of four models, three yielded significant and positive associations between dispositional autonomy and self-determined motivation for solitude, with standardized coefficients ranging from .10 to .18. The effect sizes for the observed associations across both studies were small. In one model in Study 2 where we did not find significant association between these two variables, none of the other traits yielded significant associations, aside from a gender difference that emerged. We further explored whether gender interacted with personality traits to predict the two main outcome variables but did not find evidence for the moderationg effect. Since we did not conduct power analyses to determine our sample sizes for both studies, we conducted power calculation on simulated data. This is more appropriate than performing post-hoc power analyses, which have been criticized for not providing true observed power when being conducted on data that has been collected and analysed [46]. In a series of power simulations (n = 100 simulations) looking at achieved power across sample sizes between 140 and 270 and assuming 5 to 7 data points per participant, a sample of 270 (Study 2‘s sample) should allow 80% power to detect an effect size as small as .08. We included the R code of our power simulation in our OSF folder, along with the results of our simulation.

Overall, results point to dispositional autonomy as being a modest predictor of self-determined motivation for solitude. Individuals who rated themselves as higher in the tendency to be congruent in terms of how their behavior aligns with their values and interests, as resistant to pressure from others, and as typically interested in learning more about their personal experiences and emotions, tended to approach alone time with a sense they were choicefully selecting it, and they saw this time as valuable and worthwhile. These findings shed new light on how individuals experience aloneness, further suggesting that the capacity to embrace and value time spent alone might be a function of how individuals self-regulate experiences and behaviors, more generally, rather than based more simply on preferences to be alone so as to avoid social interactions. Furthermore, they suggest that this self-regulation cannot be reduced to easily intuited personality traits such as introversion. In sum, the associations between dispositional autonomy and seeing time alone as enjoyable and valuable demonstrated the first evidence to show that solitary enjoyment related to the ability to regulate oneself in positive and self-congruent way.

These results applied an SDT perspective to better understand the relation between an autonomous personality and motivation for alone time. SDT’s conceptualization of dispositional autonomy is different from Clark and Beck’s [47] assertion about an autonomous person, one who feels more competent when achieving things alone and without the help of others. According to Clark and Beck, an autonomous personality tends to have a stronger preference for solitude and possesses a tendency to seek independence at any cost. This desire for independence and individual sense of accomplishment has been showed to breed dysphoria and loneliness [48]. In contrast to this view, dispositional autonomy from an SDT perspective is defined, as we describe above, in terms of the tendency and capacity to regulate one’s experiences in accord with closely held interests and values, instead of because one feels pressured and forced to do things that are not fully endorsed. The SDT perspective of dispositional autonomy yields a different set of predictions concerning the quality of motivation for spending time alone. As such, our findings serve to clarify the distinction between these two above-described perspectives, and showed that dispositional autonomy rooted in the SDT framework relates to healthy motivation for spending time alone, which has been showed to correlate with relational and personal well-being [9]. In the same way that SDT’s conceptualization of autonomous self-regulation does not concern with individual preferences [14], SDT’s dispositional autonomy does not relate to preference for solitude.

Another important set of findings from these two studies was the absence of evidence supporting the common belief that those who are introverted like to spend time alone. Building on the literature suggesting that extroverts enjoy social attention and thus find more time to be around other people [49], it has only been inferred rather than empirically established that those high in introversion–who spend less time in social interactions–would enjoy being alone more [39]. This inference is rooted in the conception that the lack of social engagement is equivalent to enjoyment of the opposite state—aloneness. Our research findings contradicted this idea, and were different from the findings in a recent study by Thomas et al. [50]. In their study, the authors distinguished between high-functioning (happy) and low-functioning (not-happy) introverts, while our studies did not. Whereas we did not find an association between introversion and preference for solitude, they found that both types of introverts prefer solitude more than extraverts. Low-functioning introverts were motivated to seek out solitude for not self-determined reasons due to not feeling like they belong or fit into their peer groups. As was the case in our current studies, Thomas and Azmitia [1] also did not find evidence linking introversion and self-determined motivation for solitude.

Although the assumption that introverts like to spend time alone was not supported, there is more to explore. Future research might consider when and how extraverts like to have time alone. More importantly, our present findings highlighted that one cannot rely on psychological correlates of social engagement to infer the psychological correlates of solitary enjoyment. Solitude research may be more richly advanced if researchers study time alone as a unique experience with its own particular correlates and dynamics, rather than as a derivative from the lack of enjoyment or opportunities for interpersonal interactions. In fact, just as a person can feel lonely both when spending time with others and when spending time alone [12], it is possible that personality characteristics that lead people to enjoy their time with others also predict their affinity for solitude, as was the case here for an autonomous disposition. To this end, our studies suggested that a healthy motivation for solitude might be related to an individual’s tendency to regulate their daily experiences in autonomous and choiceful ways. We recognized that, while this point has been made theoretically [25], it is important to test it empirically and that is what we attempted here.

Limitations and future directions

These findings should be understood in light of some methodological limitations. A first limitation is that we relied on an operationalization of introversion that has received several criticisms. Particularly, extraversion has historically been represented with more positively valanced items such as assertiveness, positive emotions, and excitement seeking [42]. This way of operationalizing the extraversion-introversion continuum also assumes that introversion lacks those qualities. To overcome this limitation, instead of using the NEO-PI that includes predominantly positive items to represent extraversion, we used the Big-Five Inventory, which combines both behavioral and affective contents to distinguish extraverts from introverts [42]. Nonetheless, it would be worthwhile for future research to test our hypotheses with different inventories of big-five traits.

A second limitation is that the daily diary method did not involve real-time assessments of solitary experiences. Instead, we measured participants’ retrospective evaluations of individuals’ preference and motivation for solitude at the end of each day. As such, it was not possible for us to investigate whether any situational or momentary factors that happen prior to solitude that could have contributed to participants’ preference and motivation for this time. For example, our data suggested that some individuals’ preference for solitude might vary depending on the day while others might prefer solitude more consistently across days. This means that, for some people, a moderator might explain why someone would prefer to spend time alone on a particular day, or that some kinds of events may enhance this preference. Research on solitude seeking after being ostracized [20, 51] could provide some insights here. It may be that individuals with certain personality traits might be more likely to prefer solitude after feeling ostracized or excluded by others.

A third limitation is that both studies relied on college or university samples. In this research, we recruited participants within the typical age range of those who attend universities in the United States, with a mean age of 20 years, lending caution to any generalizations to the larger population beyond young adults who attend higher education in the US. Whether education levels and different life circumstances might contribute to motivation and preference for solitude is an empirical question that warrants future research. Additionally, the dynamics of time spent alone change undoubtedly change as people get older. Older adults might find time alone more tolerable and positive [33, 34], and because of that, their personality characteristics might be more dissociated from their motivation for solitude. Attitudes toward time spent alone in older adults may also be more stable and positive over time because they have had more opportunities to structure their daily solitary experiences better in ways that work for their lifestyles and routines [33, 34].

Finally, cultural factors may also shape responding to alone experiences, for example in previous research individuals from Eastern cultures may, for example, perceive spending time alone to play different functions in their life than those from Western cultures [13]. Another study also showed that self-determined motivation for solitude might be more salient for certain cultural groups than others [3]. Future research may benefit from examining these characteristics in more culturally diverse samples.

Conclusion

Overall, the present findings across two diary studies showed that the motivation behind the time we spend alone can be affected by personality dispositions, though not necessarily the dispositions many have intuitively thought to be important. We specifically explored the role of introversion, thought by many to be associated with preferences for solitude, as well as individual differences in autonomous regulation–the propensities to behaving in self-congruent ways, take an interest in one’s emotions, and feel free from pressure. We found consistent evidence that the latter personality characteristic links to the extent to which a person sees solitude as a positive and valuable experience–one that should be pursuit for its own right. Our findings suggested that while it does not incline individuals to prefer solitude over social time, a disposition toward autonomous regulation helps individuals to endorse the value of spending time with themselves in their everyday life.

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10.1371/journal.pone.0267185.r001

Decision Letter 0

Brown

Kirk Warren

Academic Editor

2022

Kirk Warren Brown

Submission Version

18 Jun 2021

PONE-D-21-07216

Who Enjoys Solitude? Autonomous Functioning (But Not Introversion) Predicts Self-Determined Motivation (But Not Preference) for Solitude

PLOS ONE

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As we know, a disposition is a tendency to think, feel, and/or act in particular ways across a variety of situations. Thus it seems expectable that dispositional autonomy would predict daily self-determined motivation for spending time alone – that is, dispositional autonomy predicts autonomous behavior. Does this research contribute insights on autonomy and solitude beyond this expectable relation?

Concerning the samples: 1) How were sample sizes determined? Power analyses are needed here, or some other justification for the sample sizes. (2) Why were undergraduate students chosen as the population of interest (beyond convenience)?

In your tables, please specify whether you are presenting unstandardized (b) or standardized (beta) estimates. The tables present the symbol for the latter, but unless the data were standardized before analysis, I’m guessing the tables present b values.

On p. 14, there is an inconsistency between text and table in one of the lower bound CIs (-.006 versus .006). Please correct this. Also note that if the former bound is accurate, the relation you present is not reliable.

In Study 2, please clearly indicate whether and how the measures and procedure are the same as/different from those of Study 1.

In both studies, please control for sex and race in preliminary models or main analyses.

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Reviewer #1: Review for PONE-D-21-07216 Who Enjoys Solitude? Autonomous Functioning (But Not Introversion) Predicts Self- Determined Motivation (But Not Preference) for Solitude

May 18, 2021

The authors have contributed a valuable addition to the empirical literature on solitude, which is sparse. In particular, they tackle the issue of differentiating the construct of solitude from the individual difference of introversion, which as they note has often been conflated, with mixed results from previous studies. In addition, their study asserts the importance of dispositional autonomy as a factor in solitude enjoyment, a factor that has largely been overlooked in the solitude literature. I have organized my comments according to the sections of the manuscript.

Introduction:

1. A correction on Thomas & Azmitia’s (2019) findings on p. 5. The authors state that Burger’s Preference for Solitude (PSS) measure showed negative correlation with self-determined motivation for solitude, but in actuality their results showed a significant positive correlation for both emerging adults and adolescents. The PSS also correlated positively with not-self-determined motivation, indicating that the PSS does not differentiate between intrinsic/autonomous/self-determined vs. extrinsic/non-autonomous/not-self-determined motivations.

2. Please cite the study in this sentence (p. 5): “In contrast, in another study that examined preference for solitude by Burger’s operationalization and self-determined motivation for solitude from SDT perspective in older adults showed positive correlations between these two concepts.”

3. It should be noted that Burger also found a significant positive correlation between introversion and preference for solitude in his original study (1995).

4. Can the authors state their hypothesis more clearly in the following sentence (p. 7): “We predicted that extraversion-introversion dimension of big-five personality would positively relate to preference for solitude but yield non-significant association with self-determined motivation for solitude.”

The phrase “extraversion-introversion dimension” renders the hypothesis unclear. Based on their introduction, I understand them to mean that introversion will positively correlate with preference for solitude; however, the Big 5 measures extraversion (high or low), thus a positive correlation would indicate that extraverts prefer solitude. It could be restated that extraversion scores will negatively correlate with preference for solitude (and motivation for solitude). Or, clearly state that you are reverse scoring the extraversion measure, so that all extravert items are reverse coded to yield an introvert score. You mention this briefly in the Methods section, but it is so non-traditional to frame this factor as Introversion that I think it would be worth explaining more clearly to the reader. On a related note, it is troubling that introversion on the Big 5 is so negatively valenced (defined with the items of shy, reserved, inhibited, as well as low scores on all of the “positive” items). I don’t know if this affects the authors’ interpretation of their findings, but it could be worth noting (there is a long tradition of such critiques of the Big 5 for this, and other reasons, e.g. Block 1995; 2010). This is not the authors’ problem, but it could be worth mentioning as a possible explanation for why laypeople and researchers alike regularly “intuit” that introversion must be related to solitude. Perhaps it is because the Big 5 is not accurately measuring introversion – only the negative side of low extraversion.

5. To support the authors’ framing of mixed results when it comes to introversion and solitude, the authors may want to include a more recent study by Thomas and colleagues (2020), in which cluster analysis differentiated between two clusters of introverts (high-functioning and low-functioning re: measures of adjustment), and these clusters did show different associations to preference for solitude, loneliness, and motivation for solitude.

6. The rationale for their second hypothesis (dispositional autonomy) is clear and well-reasoned.

Study 1

7. I appreciate that the authors utilized a daily diary methodology for this study, as I agree these types of methods improve ecological validity in general, and in particular for assessing how people experience their time alone.

8. A minor clarification - In Weinstein et al’s original study, the measure is called the Index of Autonomous Functioning (IAF) whereas the authors of this manuscript use the term Autonomous Functioning Index (AFI). I am not sure if the name of the scale has been altered since its original publication, or whether this is an error. Please revert to IAF if necessary.

9. A couple of comments on their preference for solitude measure. I found it odd that the authors did not use Burger’s Preference for Solitude Scale in their study after discussing it in their introduction. It can be difficult to compare results between this study and prior studies if the measures are not the same. It would be helpful if the authors could include an explanation for why his original 12-item scale was not used in their initial survey, along with the other personality measures. Second, it would be helpful if the authors could briefly explain how they selected the three questions they did use to assess preference for solitude during the daily diary study. For example, were their three questions inspired by, or derived from, Burger’s measure in any way? Were they theoretically generated based on other sources?

10. Please include the rating scale used for preference for solitude. Was it 1-5? This would help readers interpret the descriptive statistics on p. 13.

11. As with point 9 above, it would be helpful to briefly explain how they selected the four questions used to assess self-determined motivation for solitude during the daily diary study.

12. In the daily diary prompts, were the self-determined motivation questions only presented to participants if they had spent time alone that day? The way these questions are worded, it sounds as if they are referencing actual time the participant had spent alone.

13. Did the study collect data on the frequency or duration of time spent alone each day? If so, that would be valuable to add into the analysis.

Study 2

14. The inclusion of all 5 factors of the Big 5 Inventory is presented, convincingly, as a worthwhile addition in order to evaluate how influential dispositional autonomy is for predicting solitude behaviors.

15. It could be worth noting that agreeableness and conscientiousness were both marginally significant (<.10). They are very close to the .05 cutoff, and very close to the introversion results. In particular the results show a trend with low agreeableness being associated with preference and motivation for solitude. Theoretically this might make sense, given that highly agreeable people may be less able to resist social pressure (one of the aspects of the IAF), so people lower in agreeableness could potentially find it easier to withdraw from the social scene (potentially disrupting social norms or social harmony) and take their alone time.

Discussion

16. Change personality types to traits. (p. 20).

17. The stronger case for self-determined motivation for solitude and positive development was found with emerging adults rather than adolescents in the Thomas & Azmitia study they reference (p. 20).

18. I found the section (p. 21-22) following this sentence particularly strong and theoretically sound: In sum, the associations between dispositional autonomy and seeing time alone as enjoyable and valuable demonstrated the first evidence to show that solitary enjoyment related to the ability to regulate oneself in positive and self-congruent way.

19. Just a side note, re: a statement on p, 23 “…it is possible that the same personality characteristics that lead people to enjoy their time with others also predict their affinity for solitude.” Maslow made the essentially same point in his studies of self-actualization, when he noted that self-actualized people have both a love of privacy and a love of other people.

20. On p. 23, “To date, we are aware of no empirical data that has directly assessed the link between any personality characteristics…” but didn’t both Burger (1995) and Thomas and colleagues (2019; 2020) include introversion-extroversion data in relation to preference for solitude and motivation for solitude? See points 3 and 5, above. But, to the authors’ point, this study does appear to be the first that shows the links between the personality characteristic of autonomous functioning and solitude.

Proofreading:

The authors will want to proofread for typos, as there were many in the manuscript. A few examples, although I didn’t document them all: “I do thinks in order to avoid feeling ashamed” (p. 11); “Sixteen participants who filled out the initial survey did not the diary portion of the study…” (p. 16); “ First, all two studies relied on” (p. 23); etc.

Figures 1 and 2 have the same title. Can the authors add “in Study 1” to Figure 1 and “in Study 2” in Figure 2 (or something to that effect) so that the figures are differentiated?

Reviewer #2: This study differentiated between daily preference for solitude and daily self-determined motivation for solitude by linking the latter, and not the former, with trait-level autonomy. This study has the potential to contribute to the literature by demonstrating a link between self-determined motivation for solitude and the well-established personality factor of autonomy based on SDT. However, certain issues came up in my reading, mainly having to do with the data analysis, that I think would need to be addressed to prepare this paper for publication.

I commend the authors for posting their Rmarkdown code and data files on OSF. These were also very helpful to me in checking my own understanding of what the authors had done.

Introduction

1. Could the Introduction section explain further why introversion and autonomy were selected as measures for establishing discriminant validity of preference for solitude & self-determined motivation for solitude? (As opposed to other aspects of personality such as dispositional shyness, attachment styles, low sensation-seeking, etc.)? The Discussion section clearly explains the rationale for personality variable selection, but it is less clear from the Introduction section.

2. Since the Thomas & Azmitia motivation for solitude scale also includes a measure of not-self-determined motivation for solitude, I am curious why this scale was not included in the study (as another contrast to preference for solitude)?

3. I am a bit confused by the rationale for hypothesizing that introversion would show no association with self-determined motivation for solitude. The Leary et al. (2003) study cited in this section suggests the opposite, that that individuals low in characteristics related to extraversion/sociability/people orientation derive more enjoyment from engaging in activities alone than individuals high in these extraverted traits. Since other cited research is inconclusive on this, it seems that, on balance, the suggestion is that individuals higher in introversion might derive more enjoyment from solitary activities. What was the basis for the hypothesized null effect?

Method (Studies 1 and 2)

4. How was alpha (reliability) computed for daily-level preference for solitude and self-determined motivation for solitude? It appears from the study R code posted on OSF that Cronbach’s alpha is computed for level-1 and level-2 variables in the same manner. However, it is problematic to use Cronbach’s alpha directly on repeated measures data because it does not account for person-level clustering. The psych::multilevel.reliability function in R can be used to calculate reliability for a 2-level model (Nezlek, 2017).

Nezlek, J. B. (2017). A practical guide to understanding reliability in studies of within-person variability. Journal of Research in Personality, 69, 149-155.

5. Please specify the scale for the daily preference for solitude measure (Study 1 Method section). The description of the self-determined motivation for solitude measure is also not entirely clear. Did participants respond to this measure for each solitary event they reported, or was it administered once for the entire day? It is stated that “Scores on each item were averaged for both solitary episodes” so it sounds like two solitary episodes are used? (This is not explained)

6. The paper refers to random slopes for introversion, and random slopes for autonomy. However, in a model with 2 levels (level 1 = daily diaries, level 2 = people), level-2 predictors don’t have random slopes across people; rather, there is a fixed-effect slope that applies to the whole sample.

For example, for the autonomy-motivation for solitude slope, because each person only contributes a single autonomy score, it is not possible to compute a slope for each person. There is just an autonomy-motivation for solitude slope which applies to the entire sample, and which reflects the association between trait autonomy and each person’s mean motivation for solitude score across all study days. (If autonomy had been measured repeatedly at the daily level, it could have a random slope with motivation for solitude that varied across participants).

This leaves me confused about what is meant to be captured in Figures 1 and 2. If each person only provided one score for dispositional autonomy, how can a slope between this and any other variable be computed for a single person? It is possible that I am entirely misinterpreting what the authors intended to model.

In the R code posted on OSF, the level 2 variables have been added as random effects to this models; these models appear to have been mis-specified (or I have no idea what these random effects are modeling). Again, it is possible that I misunderstood what the authors intended to do.

7. More broadly, since the study hypotheses are not about any within-person associations, there seems to really be no need to do mixed-effects or multilevel modeling. Since all model predictors are at level-2 (person-level), their regression coefficients just reflect associations between the person-level predictor (e.g. trait autonomy) and each person’s mean of the daily-level outcome variable (e.g. each person’s mean motivation for solitude score across study days).

Results and Discussion

8. The results sections state for example that “Random-intercept models without fixed effects revealed an ICC of…” (p. 13). Do the authors mean “random-intercept models with no predictors”? When computing ICC, there should still be a fixed effect for the intercept. (The lmer function in R will also add a fixed intercept by default even if it’s not included in the model syntax).

9. For Study 2, did the authors have any specific hypotheses regarding associations between other personality factors (neuroticism, agreeableness, etc.) and daily measures of solitude preferences/motivation? The Discussion section should also say more about these associations and about the significant association between agreeableness and preference for solitude. Also, why was openness to experience excluded from the models reported in Tables 3 and 4?

10. The Results and Discussion sections refer to correlations between dispositional autonomy and self-determined motivation for solitude. Since mixed-effects regression models with control variables were used in analyses, it is not precise to refer to these relationships as correlations (this usually implies bivariate correlations at a single level). Terms such as “associations” or “relationships” could be used instead.

11. In the limitations section, it is stated, “Older adults might find time alone more tolerable (22), and therefore, their personality might affect motivation for solitude less strongly. Nonetheless, given that motivation and preference for solitude in young adults is more likely to vary daily whereas attitudes toward time spent alone in older adults remained more stable and positive over time…” Could the authors explain this further? Why would higher overall levels of preference for solitude in old age necessarily lead to reduced within-person variability in preference for solitude?

12. The study limitations section is limited in that in only mentions limitations related to the characteristics of the participant sample. Could the authors also address potential limitations of the study design, measures, etc.?

Minor comments

13. The Methods and Results section headings should specify whether they’re referring to Study 1 or Study 2 (to avoid ambiguity)

14. On p. 5: “In contrast, in another study that examined preference for solitude by Burger’s operationalization and self-determined motivation for solitude from SDT perspective in older adults showed positive correlations between these two concepts.” Which study is this sentence referring to? And in which age group? The implication in this paragraph is that mixed findings may be due to different motivations across age groups, but it is not clear exactly where this conclusion comes from.

15. In the study 1 Participants section (p. 9), it is stated “One hundred and eighty three undergraduate students (153 females; 9% Hispanic), and then it is stated, “The sample consisted of 53% Whites and Caucasians, 35% Asians or Pacific Islanders, 5% Black or African Americans, …” This double description of the sample ethnic make-up is a bit confusing as they do not match.

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Reviewer #1: No

Reviewer #2: No

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Attachment

Submitted filename: Review for PONE.docx

10.1371/journal.pone.0267185.r002

Author response to Decision Letter 0

Submission Version

15 Nov 2021

Dear Dr. Brown,

Thank you for your feedback on our earlier draft of the manuscript: “Who Enjoys Solitude? Autonomous Functioning (But Not Introversion) Predicts Self-Determined Motivation (But Not Preference) for Solitude” (PONE-D-21-07216) and for soliciting feedback from the two expert reviewers. Your and reviewer comments were very helpful, and we have thought carefully about each and how to best undertake any improvements to the paper. We detail each below in bolded font, and our response to it.

Editor Comments

1. As we know, a disposition is a tendency to think, feel, and/or act in particular ways across a variety of situations. Thus it seems expectable that dispositional autonomy would predict daily self-determined motivation for spending time alone – that is, dispositional autonomy predicts autonomous behavior. Does this research contribute insights on autonomy and solitude beyond this expectable relation?

Response. Thank you for this comment. We thought long and hard about the implications of this issue, as it speaks directly to how clearly we had communicated the theoretical contribution of the paper in the previous version of the manuscript. We concluded that two elements of the work must be brought out, and have made some revision in the Introduction to emphasize the following contributions:

First, our paper was the first to explicitly state the conceptual distinction between the two concepts, preference for solitude and self-determined motivation for solitude. The two literatures have existed in parallel, but though they are understood to be conceptually distinct, they have not been tested in parallel for the purpose of clarifying how or why they are different. We have tried to do that here by examining their distinct relations with personality predictors. To help make this point, we have added text throughout the Introduction and Discussion. For example, we now start with an organizing paragraph new to this version:

“Evidence is mounting that self-determined motivation for solitude is empirically distinct from merely preferring solitude over social time (1, 9, 10), but there is little knowledge about what drives people to self-determined motivation for solitude, even when they do not necessarily prefer to be alone. In this paper, we explore the role that personality plays in both motivation and preference for solitude, focusing on two personality characteristics that should predict the two constructs differentially: autonomous orientation, which is likely to drive self-determined motivation, and introversion, likely to drive preference” (p. 3)

Second, we have added the paragraph below to the Introduction to highlight that the conceptual work which aims to understand whether a disposition that differentiate between those who self-regulate and those who do not (i.e., autonomous orientation), can explain healthy motivation toward a self-connecting experience that is commonly portrayed as challenging (with solitude being a prime example).

“Previous literature has demonstrated that those who tend behave in ways that are consistent with their beliefs and values tend to be motivated by intrinsic and self-determined reasons in whatever they do (36,37,39). However, it is important to highlight that solitude is commonly portrayed as a challenging experience for people. This is particularly relevant for young adults because they find solitude more difficult than older age groups (24,40) unless they have been allowed opportunities to develop a capacity to enjoy it. Given this, an investigation of dispositional autonomy that represents that capacity speaks to Winnicott’s theorizing (32) discussed above, which has not been considered in previous studies.”(p. x)

In this paper, we sought to highlight the theoretical underpinning of this investigation – the proposition of Donald Winnicott around the capacity to be alone and how this capacity can be nurtured through development. We believe this work investigates a concept that is similar to that capacity of which Winnicott speaks. We explained Donald Winnicott’s capacity to be alone in an earlier section of the Introduction on p. 8.

2. Concerning the samples: 1) How were sample sizes determined? Power analyses are needed here, or some other justification for the sample sizes. (2) Why were undergraduate students chosen as the population of interest (beyond convenience)?

Response. We now state in the Method of Studies 1 (p. 10) and 2 (p. 17) the rationales behind our sample size. We believe it is justified to determine sample sizes based on realistic measures: expectations of how many participants we can recruit from the pool and lack of external funding to recruit outside of this pool.

We also wrote now: “We selected to test study hypotheses with students because we could access and track this population; however, it is worth noting that this age group – representing emerging adulthood – have been the focus of past research which has found robust links between self-determined motivation and well-being in solitude (Nguyen et al., 2018; Thomas & Azmitia, 2018), giving added value to our current tests of antecedents of self-determined motivation.” (p. 10)

3. In your tables, please specify whether you are presenting unstandardized (b) or standardized (beta) estimates. The tables present the symbol for the latter, but unless the data were standardized before analysis, I’m guessing the tables present b values.

Response. We now present both unstandardized (b) and standardized (beta or ß) estimates within the tables.

4. On p. 14, there is an inconsistency between text and table in one of the lower bound CIs (-.006 versus .006). Please correct this. Also note that if the former bound is accurate, the relation you present is not reliable.

Response. Thank you for identifying this error. You are correct – both should have been .006. However, following Reviewer 2’s comment, we have fixed the errors in our analyses – removing random slopes because they should not be included in the models. Therefore, we have produced new tables (Tables 1-4) which present the main analyses of the two studies.

5. In Study 2, please clearly indicate whether and how the measures and procedure are the same as/different from those of Study 1

Response. On p. 17 of the manuscript, we now clarify that the measures and procedures are identical to those of Study 1, except that in study 2 we measured all five personality traits.

6. In both studies, please control for sex and race in preliminary models or main analyses.

Response. We have now added gender and ethnicity to the secondary models (presented on the right side of each Table 1-4), with these two predictors included as covariates in all the confirmatory analyses.

REVIEWER 1

Response. Thank you for this catch. We have now made this change on p. 6 of the manuscript. It now reads: “Burger’s 12-item measure of preference for solitude (17) showed positive correlations with both measures that Thomas and Azmitia (1) used to assess self-determined and not-self-determined motivation for solitude in late adolescence. Another study that examined preference for solitude in adults older than 35 years of age showed positive correlation between Burger’s preference for solitude scale and measure of self-determined motivation for solitude, yet negative correlation between preference and measure of not self-determined motivation for solitude (23). These correlations suggest that, for those beyond adolescence and young adulthood, preference for solitude is associated more with self-determined rather than not-self-determined motivation for solitude, whereas preference for solitude in late adolescence could reflect both types of motivation. From this set of mixed results, it is possible that preference for solitude is motivated differently across age groups (24) and might have varied psychosocial implications for the individuals that prefer to be alone (25).”

Response. We now cited the sentence referring to the work by Weinstein and Nguyen (2021) (citation #10) which included the correlations between preference for solitude and both types of motivation (i.e., identified as equivalent to self-determined motivation for solitude, external as equivalent to not-self-determined motivation for solitude).

3. It should be noted that Burger also found a significant positive correlation between introversion and preference for solitude in his original study (1995).

Response. We have now included Burger’s finding concerning the significant positive correlation to the Introduction under the section discussing the association between introversion and preference for solitude on p. 6 (citation #17).

Response. We have now rewritten the hypothesis so that it is clearer: “we predicted that higher scores on introversion would positively relate to higher ratings of daily preference for solitude. In this research, we operationalized introversion as having the opposites qualities with those that are often associated with extraversion; that is, introverts are someone who tend to be more reserved, quieter, less talkative, energetic, or assertive. We will describe how we assess introversion in the method section.” (p. 10).

On a related note, it is troubling that introversion on the Big 5 is so negatively valenced (defined with the items of shy, reserved, inhibited, as well as low scores on all of the “positive” items). I don’t know if this affects the authors’ interpretation of their findings, but it could be worth noting (there is a long tradition of such critiques of the Big 5 for this, and other reasons, e.g. Block 1995; 2010). This is not the authors’ problem, but it could be worth mentioning as a possible explanation for why laypeople and researchers alike regularly “intuit” that introversion must be related to solitude. Perhaps it is because the Big 5 is not accurately measuring introversion – only the negative side of low extraversion.

Response. The reviewer is absolutely correct about this typical problem with operationalizations of introversion. We have now clarified our own operationalization and measure of introversion in two places, which includes both positive and negative characteristics:

1. One at the end of p. 10 in the Introduction where we state our hypothesis for introversion:

“In this research, we operationalized introversion as having the opposite qualities with those that are often associated with extraversion; that is, introverts are someone who tend to be more reserved, quieter, less talkative, energetic, or assertive. We will describe how we assess introversion in the method section.”

2. The second place is in the Method section, on pp. 13-14, where we describe our measure:

“To measure introversion, we used the eight items from John and Srivastava’s (41) Big Five Inventory (BFI) that were used to measure the big-five trait of extraversion. This measure includes descriptive statements of how extraverts often behave, such as being “talkative” and “full of energy”. We used this instead of the NEO-PI (Neuroticism, Extraversion, Openness Personality Inventory, 41) because the NEO-PI includes positive emotions and warmth as descriptors of extraversion, which could potentially portray introversion as lacking those positive qualities (see comparison between NEO-PI and BFI in Zillig et al (42)). Using the BFI Extraversion subscale, we showed participants a stem stating, “I see myself as someone who…”, and they proceeded to rate their agreement to a series of descriptive statements. We reverse-coded the extraversion-related items like “talkative” and “full of energy”, and averaged them with items included “reserved” and “quiet”, such that higher overall scores reflected introversion (α = .87). Participants rated their responses on a 5-point Likert scale, ranging from 1 = “strongly disagree” to 5 = “strongly agree”. ”

3. The third place is in the Limitations and Future Direction, on p. 26, where we addressed the limitation of existing measures of extraversion-introversion dimension:

“A first limitation is that we relied on an operationalization of introversion that has received several criticisms. Particularly, extraversion has historically been represented with more positively valanced items such as assertiveness, positive emotions, and excitement seeking (42); this assumes introversion lacks those qualities. To overcome this limitation, instead of using the NEO-PI that includes predominantly positive items to represent extraversion, we used the Big-Five Inventory, which combines both behavioral and affective contents to distinguish extraverts from introverts (42). Nonetheless, it would be worthwhile for future research to test our hypotheses with a wide range of different inventories of big-five traits.”

Response. We agree that Thomas et al. (2020) would be a valuable addition to this paper. We have now cited the authors in the Discussion. We see that Thomas et al. (2020)’s findings are still different from our finding. Although we did not find the association between introversion and preference for solitude, Thomas et al. (2020) found that both low- and high-functioning introvert clusters had higher scores on preference for solitude than the extravert cluster. Therefore, we included this in the Discussion on p. 24 as follow:

“Our research contradicted such misconception and were different from the findings by a recent study by Thomas et al (50). In their study, they distinguished between high-functioning (happy introverts) and low-functioning introverts (not-happy introverts), while our studies did not. Whereas we did not find correlation between introversion and preference for solitude, they found that both types of introverts prefer solitude more than extraverts. Low-functioning introverts were motivated to seek out solitude for not self-determined reasons due to not feeling like they belong or fit into their peer groups. However, their findings also did not find evidence that both groups of introverts showed more self-determined motivation for solitude than extraverts.”

Response. We are glad that the reviewer agrees with our choice of research design as we believe this methodology allows for more precise assessments of people’s daily experiences with solitude.

Response. We have now changed the name of the scale to the original IAF.

Response. We have now elaborated on the existing text to describe the source of items and our decision-making process in selecting this source within the Method section on p. 14. To summarize here, we were inspired by a short measure used by Wang et al. (2013) and felt that their items were more appropriate for our daily diary design and operationalization of preference for solitude; that is, we are interested in whether participants would rather spend time alone more than with other people on a specific day. We felt that Burger’s measure conflates preference and desire with enjoyment and benefits of solitude. This is the paragraph we added to p. 14:

“We decided to use this measure rather than Burger’s preference for solitude (17) because Wang et al.’s measure is shorter and thus more appropriate for daily diary design. Further, Burger’s measure includes some items that describe specific situations that might not apply to our participants’ daily experiences, such as “I like to vacation in places where there are few people around and a lot of serenity and quiet” or “If I were to take a several-hour plane trip, I would like to sit next to someone who was pleasant to talk with”. Some of Burger’s items also conflate preference and desire to be alone with enjoyment and benefits of being alone (i.e., “I enjoy being by myself”, Time spent alone is often productive for me”). Because we aimed to distinguish preference and desire from motivation to be alone for the enjoyment and benefits of solitude, we opted not to include those items in our measure.”

10. Please include the rating scale used for preference for solitude. Was it 1-5? This would help readers interpret the descriptive statistics on p. 13.

Response. We have now added this detail to the description of the scale. The items were rated on 7-point scale (from 1 = not at all true to 7 = very true) to keep it consistent with the measure of self-determined motivation for solitude.

11. As with point 9 above, it would be helpful to briefly explain how they selected the four questions used to assess self-determined motivation for solitude during the daily diary study.

Response. We have now described the source of items for assessing self-determined motivation for solitude in the Method section on p. 15. Namely, we used the items developed by Nguyen et al. (2018) rather than Thomas and Azmitia (2019)’s measure because it offered a better fit for measuring daily solitude expeirence. We detail the reasons for this in the same paragraph:

“For this variable, we used the scale from Nguyen et al. (2), which we felt was more appropriate for a diary study design because it measures state-level motivation for solitude and could better capture day-to-day fluctuation. In comparison, the measure developed by Thomas and Azmitia (1) is more appropriate for distinguishing individual differences in self-determined motivation for solitude.” (p. 14)

Response. Questions assessing self-determined motivation asked participants about all the instances they were by themselves on that day, so they were not about any specific time participants had spent alone. The participants were presented with a prompt, which has now been added to the description of the scale on p. 14: “Different people spend time by themselves for different reasons. Please indicate the extent to which each of the following reasons applies to you regarding all the instances when you were by yourself today”

13. Did the study collect data on the frequency or duration of time spent alone each day? If so, that would be valuable to add into the analysis.

Response. The study did not involve data collection on frequency or duration of time spent alone. We were mainly interested in the two measures of preference for solitude and self-determined motivation for solitude.

Response. Thank you for this comment.

Response. We thank the Reviewer for this suggestion. However, we opted not to interpret marginally significant results, particularly for associations that we did not a-priori hypotheses for. We made this choice to avoid over-interpreting results that could be spurious.

16. Change personality types to traits. (p. 20).

Response. We have made this change.

17. The stronger case for self-determined motivation for solitude and positive development was found with emerging adults rather than adolescents in the Thomas & Azmitia study they reference (p. 20).

Response. Thank you for spotting this. We have made this change on p. 8, referencing Thomas & Azmitia (2019)

“Indeed, this view of healthy motivation for solitude has been reflected in recent empirical works, which showed that the pursuit of solitude for its benefits to creativity and relaxation was linked to experiences of personal growth in young adults (1).”

Response. Thank you for this. We are glad the Reviewer agrees with our interpretation.

Response. Thank you for this positive comment. We agree that dispositional autonomy is very conceptually close to the notion of self-actualized person by Maslow. In fact, Maslow’s theory around self-actualization was cited often in self-determination theory works and contributed to SDT formation. The argument of how the two conceptualizations of an autonomous person and a self-actuazlied person are connected has been demonstrated elsewhere (e.g., Sheldon & Kasser, 1995) and is outside the scope of this paper so we have opted not to refer to Maslow in our manuscript.

Sheldon, K. M., & Kasser, T. (1995). Coherence and congruence: Two aspects of personality integration. Journal of personality and social psychology, 68(3), 531.

Response. We have now removed this sentence.

Figures 1 and 2 have the same title. Can the authors add “in Study 1” to Figure 1 and “in Study 2” in Figure 2 (or something to that effect) so that the figures are differentiated?

Response. Following Reviewer 2’s comments (described below), Figure 1 and Figure 2 are no longer needed for this manuscript.

REVIEWER 2

This study differentiated between daily preference for solitude and daily self-determined motivation for solitude by linking the latter, and not the former, with trait-level autonomy. This study has the potential to contribute to the literature by demonstrating a link between self-determined motivation for solitude and the well-established personality factor of autonomy based on SDT. However, certain issues came up in my reading, mainly having to do with the data analysis, that I think would need to be addressed to prepare this paper for publication.

I commend the authors for posting their Rmarkdown code and data files on OSF. These were also very helpful to me in checking my own understanding of what the authors had done.

Response. We now have elaborated in the Introduction more clearly why we were interested in comparing the different effects of both introversion and dispositional autonomy (also in response to Editor Comment 1). Along with a new opening paragraph (p. 3), the rationale for testing introversion was explained in pp. 6-7. For one, we highlight the mixed findings in previous literature regarding the association between introversion and perceiving solitude as enjoyable. Based on these mixed results, we predicted the positive correlation between introversion and preference for solitude, but made no such prediction for self-determined motivation for solitude. The rationale for looking at dispositional autonomy was explained on pp. 7-9. To do so, we described theoretical views of Donald Winnicott regarding the capacity to be alone (p. 7), and we also highlight why autonomous disposition, here tested through interest-taking, self-congruence, and freedom from pressure may make it easier and more appealing to be alone with one’self’ (p. 8).

Response. We had some hesitation around the measure of not self-determined motivation for solitude by Thomas and Azmitia because this measure include items that might touch on social anxiety (i.e., “I feel anxious when I’m with others”), and lack of belonging (i.e. “I don’t feel liked when I’m with others”, “I feel like I don’t belong when I’m with others”). That framing is not within the scope of this manuscript, which was instead interested more specifically in seeing value and personal reward in solitude. This is the reason we did not use that subscale and focused on distinguished between preference for solitude and self-determined motivation for solitude.

Response. The rationales for not predicting the association between introversion and self-determined motivation for solitude were explained on p. 10, after highlighting the theoretical argument for why introversion may relate to preference, but not self-determined motivation, for solitude.

To do this, we described the findings that showed positive correlation between introversion and preference for solitude and general positive attitudes toward solitude in cross-sectional design. However, these findings were interpreted to mean that introverts enjoy solitude more than extraverts. Then, we described findings that tracked day-to-day experiences with solitude and showed that extraverts actually rated both social and solitary experiences positively, and introverts also felt less positive than extraverts when not interacting with other people. Therefore, introverts might spend more time alone and might generally report preferring being alone more, that does not mean they enjoy solitude more or seek it out because of its enjoyment. On p. 10 we write:

“However, while Burger (17) and Leary et al. (21) used one-time measures of people’s evaluations of their own personality and attitudes toward solitude, a study by Srivastava et al. (29), which used day-construction design and collected data from participants’ day-to-day experiences, showed a different pattern. When asked to report levels of positive affect when interacting with other people and when not interacting, those high in extraversion reported feeling more positive in both types of experiences. Interestingly, those low in extraversion also felt more positive in social interaction than when not interacting, and in fact felt less positive than extraverts when not interacting with others. This presents an interesting picture for introverts when it comes to their time spent alone; they generally show a greater preference for solitude than extraverts, (1) because they do not derive as much benefit out of social interactions as extraverts, but they might not necessarily enjoy time alone more (30). In other words, introverts’ preference for solitude might be driven more by the lack of appeal held by available social experiences, and less by their anticipation that spending time alone would be enjoyable.”

Nezlek, J. B. (2017). A practical guide to understanding reliability in studies of within-person variability. Journal of Research in Personality, 69, 149-155.

Response. We greatly appreciated this suggestion by the Reviewer. We have now reported reliability across all items and assessment (days within person) for preference for solitude and self-determined motivation for solitude. Further, we also included Scale Reliability section for both studies to describe the variance components at different levels (i.e., item, day, person). You can also see percentages of variance at each level in all the tables (Table 1-2 for Study 1; Tables 3-4 for Study 2).

Response. We have now added this detail to the description of the scale. Specifically, we describe that the items were rated on 7-point scale (from 1 = not at all true to 7 = very true) to keep it consistent with the measure of self-determined motivation for solitude. Participants responded to items in both measures once for the entire day; that means, the measures assess participants’ evaluations of their solitary experiences in general on each day. The statement “Scores on each item were averaged for both solitary episodes” was included by mistake. We apologized for this mistake and were grateful that the Reviewer had picked up this error; we have checked our codebook and removed this statement.

Response. Again, we are grateful for this comment because the Reviewer was right to point out that random slopes should not be included, since there is no way for each participant to have their own slope for personality differences predicting daily preference and motivation. This was entirely our misunderstanding of the data structure. We have consulted with a statistics expert that is more familiar with multilevel data and they have made the same suggestion: to only conduct random-intercept models for both outcomes. We have corrected this accordingly. You now can find our description of the models for Study 1 on p. 17 and Study 2 on p. 20.

Response. This is correct. We have corrected our description of the models and also reran the analyses. The new analyses do not change the conclusions of the study, and new analyses are now summarized in Tables 1 and 4 and described in the text of Study 1 (p. 16) and 2 (p. 18) Results sections.

Response. Thank you for this. We have now removed this statement.

Response. We did not have any specific hypotheses regarding associations between other big-5 personality factors. We included all big-5 traits in Study 2 following a review round at the journal where we previously submitted this work as the previous reviewers felt that it would give stronger evidence for whether these two characteristics of interest predicted the outcomes when all big-5 traits were included. Reviewer 1 also agreed with this decision and thought the addition of all big-5 factors was appropriate. However, because we did not make any a-priori predictions for those factors, we preferred not to try and interpret them after the fact.

Furthermore, the missing of openness in one of the models was a mistake on our part. Thank you for spotting this. We now have added results of openness to Tables 3 and 4.

Response. We have now used the term “association” instead of “correlation” to describe our results.

Response. We now have added this explanation to clarify the age differences (p. x):

“Nonetheless, given that motivation and preference for solitude in young adults are more likely to vary daily depending situations preceding solitude (i.e., after being ostracized; 18), the samples or our studies were appropriate for an investigation of how motivation and preference fluctuate on a day-to-day basis. On the other hand, attitudes toward time spent alone in older adults remained more stable and positive over time because they have had more opportunities to structure their daily solitary experiences better in ways that work for their lifestyles and routines (24).”

Response. We have now done this. Specifically, we discussed the limitation of not including real-time assessments of solitary experiences in the paragraph on page 27:

“A second limitation is that the daily diary method did not involve real-time assessments of solitary experiences. Instead, we measured participants’ retrospective evaluations of individuals’ preference and motivation for solitude at the end of each day. As such, it was not possible for us to investigate whether any situational or momentary factors that happen prior to solitude that could have contributed to participants’ preference and motivation for this time. For example, our data suggested that some individuals’ preference for solitude might vary depending on the day while others might prefer solitude more consistently across days. This means that, for some people, a moderator might explain why someone would prefer to spend time alone on a particular day, or that some kinds of events may enhance this preference. Research on solitude seeking after being ostracized (20,45) could provide some insights here. It may be that individuals with certain personality traits might be more likely to prefer solitude after feeling ostracized or excluded by others.”

13. The Methods and Results section headings should specify whether they’re referring to Study 1 or Study 2 (to avoid ambiguity)

Response. We have now done this. For example, Method now reads “Study 1 Method”

Response. The sentence now reads: “Another study that examined preference for solitude in adults older than 35 years of age showed positive correlation between Burger’s preference for solitude scale and measure of self-determined motivation for solitude, yet negative correlation between preference and measure of not self-determined motivation for solitude (23)” to elaborate on the details of the study. We have also added the citation 23 on p. 5.

23. Weinstein N, Nguyen TT. Motivation and preference in isolation: A test of their different influences on responses to self-isolation during the COVID-19 outbreak. R Soc Open Sci. 2020;7(5).

Response. Thank you, good point. We have removed this other statistic as it was not accurate.

In summary, we are grateful for the constructive feedback we received from the editor and both reviewers. Their views helped us to clarify, elaborate, and correct text in key places that improved how we communicated the conceptual approach of the project, methodological decisions made, and analytic decisions and findings. We find the revised manuscript is much improved and hope that readers see the same.

Sincerely,

Thuy-vy T. Nguyen

Netta Weinstein

Richard M. Ryan

10.1371/journal.pone.0267185.r003

Decision Letter 1

Brown

Kirk Warren

Academic Editor

2022

Kirk Warren Brown

Submission Version

20 Jan 2022

PONE-D-21-07216R1Who Enjoys Solitude? Autonomous Functioning (But Not Introversion) Predicts Self-Determined Motivation (But Not Preference) for SolitudePLOS ONE

Dear Dr. Nguyen,

Thank you for re-submitting your manuscript to PLOS ONE. After careful consideration, we still feel that the paper has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during this round of the review process. The issues with the paper on this round are mostly mine, and reflect ongoing concerns with your sample size and population.

In the previous round, I asked: 1) How were sample sizes determined? Power analyses are needed here, or some other justification for the sample sizes. (2) Why were undergraduate students chosen as the population of interest (beyond convenience)?

In response to question 1, you responded that “We believe it is justified to determine sample sizes based on realistic measures: expectations of how many participants we can recruit from the pool and lack of external funding to recruit outside of this pool.”

This explanation is inadequate. Consider a study that drew from a very small pool of participants and had no funding support, permitting a recruitment of 10 people. Would this be sufficient justification for that sample size? I think not. If your studies are not appropriately powered the reader doesn't know how reliable the findings are. This casts your study findings into considerable doubt. The lack of power analyses for both studies, and the consequences thereof, should be clearly acknowledged in your General Discussion.

In response to my question 2, you stated that: “We selected to test study hypotheses with students because we could access and track this population; however, it is worth noting that this age group – representing emerging adulthood – have been the focus of past research which has found robust links between self-determined motivation and well-being in solitude...”

While I find your rationale sensible, it doesn't account for the fact that students may be a poorly generalizable population in which to address the study questions. I recommend that you acknowledge the limitations of college student sampling in your General Discussion.

Please also address the comments of Reviewer 1, who asks for clarification on several points.

While I am calling this a minor revision, your attention to these issues will determine the final decision on the manuscript.

Please submit your revised manuscript by Mar 06 2022 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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We look forward to receiving your revised manuscript.

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Kirk Warren Brown

Academic Editor

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Yes

Reviewer #2: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

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4. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #1: Yes

Reviewer #2: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #1: Yes

Reviewer #2: Yes

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6. Review Comments to the Author

Reviewer #1: Thank you to the authors for adequately addressing my comments and questions in the first round of reviews. Two minor comments/edits: 1) It's still not clear in the Procedure section of Study 1 what measures or questions were asked in the daily surveys. The initial survey is clearly explained, but I have to infer what was asked in the daily surveys. The statement on p. 14 under "Diary Survey" is a bit vague ("For each diary surveys [sic], participants reported the events that happened to them that day, including their experiences with social and solitary experiences.") and I had to assume that the measures for dispositional autonomy and introversion measures were included in each daily survey, but this was not explicitly stated. 2) Change AFI to IAF on p. 13.

Reviewer #2: Thank you for thoroughly addressing my comments in this revision - I have no further concerns. The manuscript was a pleasure to read and I think it makes a valuable contribution to our understanding of the role of autonomous functioning in motivation for solitude.

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Reviewer #1: No

Reviewer #2: Yes: Jennifer Lay

10.1371/journal.pone.0267185.r004

Author response to Decision Letter 1

Submission Version

23 Mar 2022

Sample size justification

The Editor commented:

“We believe it is justified to determine sample sizes based on realistic measures: expectations of how many participants we can recruit from the pool and lack of external funding to recruit outside of this pool.” This explanation is inadequate. Consider a study that drew from a very small pool of participants and had no funding support, permitting a recruitment of 10 people. Would this be sufficient justification for that sample size? I think not. If your studies are not appropriately powered the reader doesn't know how reliable the findings are. This casts your study findings into considerable doubt. The lack of power analyses for both studies, and the consequences thereof, should be clearly acknowledged in your General Discussion.

Response: Since I did not run power analysis to determine our sample sizes for Study 1 and Study 2, I conducted power simulations to examine what is the smallest detectable effect size, given multiple possible sample sizes. I have now added this in the Discussion on page 24: “Since we did not conduct power analyses to determine our sample sizes for both studies, we conducted power calculation on simulated data. This is more appropriate than performing post-hoc power analyses, which have been criticized for not providing true observed power when being conducted on data that has been collected and analysed (47). In a series of power simulations (n = 100 simulations) looking at achieved power across sample sizes between 140 and 270 and assuming 5 to 7 data points per participant, a sample of 270 (Study 2’s sample) should allow 80% power to detect an effect size as small as .08.”

Reference: Zhang Y, Hedo R, Rivera A, Rull R, Richardson S, Tu XM. Post hoc power analysis: Is it an informative and meaningful analysis? Gen Psychiatry. 2019;32(4):3–6.

The Editor commented:

Response: I have now strengthened this point in the General Discussion on page 28: “A third limitation is that both studies relied on college or university samples. In this research, we recruited participants within the typical age range of those who attend universities in the United States, with a mean age of 20 years, lending caution to any generalizations to the larger population beyond young adults who attend higher education in the US. Whether education levels and different life circumstances might contribute to motivation and preference for solitude is an empirical question that warrants future research.”

Finally, Reviewer 1 commented:

“1) It's still not clear in the Procedure section of Study 1 what measures or questions were asked in the daily surveys. The initial survey is clearly explained, but I have to infer what was asked in the daily surveys. The statement on p. 14 under "Diary Survey" is a bit vague ("For each diary surveys [sic], participants reported the events that happened to them that day, including their experiences with social and solitary experiences.") and I had to assume that the measures for dispositional autonomy and introversion measures were included in each daily survey, but this was not explicitly stated. 2) Change AFI to IAF on p. 13.”

Response: I have added more details to the Procedure section of Study 1 on page 14: “For each diary survey, participants were asked about a significant event that happened to them that day, their experiences of such event (e.g., autonomy, need satisfaction, positive and negative affect), their self-determined motivation for solitude and levels of preference for solitude. Only self-determined motivation for solitude and preference for solitude were the variables of interest for this present paper, whereas other questions were part of a separate project studying the link between daily positive events and later memories of such events.”

For the measures for dispositional autonomy and introversion measures, I believe the reviewer might have missed what I said on page 13: “All participants were enrolled after submitting an initial survey. Included in the initial survey were several personality measures, including the Introversion subscale from the Big-Five Inventory (40) and the Index of Autonomous Functioning (IAF) (27). Descriptions of personality measures used in this study are provided below.”

I hope those revisions are sufficient in addressing the comments. I am looking forward to any further feedback to help improve this manuscript.

Sincerely,

Thuy-vy Nguyen

Attachment

Submitted filename: Responses to editor and reviewers comments.docx

10.1371/journal.pone.0267185.r005

Decision Letter 2

Brown

Kirk Warren

Academic Editor

2022

Kirk Warren Brown

Submission Version

5 Apr 2022

Who Enjoys Solitude? Autonomous Functioning (But Not Introversion) Predicts Self-Determined Motivation (But Not Preference) for Solitude

PONE-D-21-07216R2

Dear Dr. Nguyen,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Kirk Warren Brown

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

10.1371/journal.pone.0267185.r006

Acceptance letter

Brown

Kirk Warren

Academic Editor

2022

Kirk Warren Brown

4 May 2022

PONE-D-21-07216R2

Who Enjoys Solitude? Autonomous Functioning (But Not Introversion) Predicts Self-Determined Motivation (But Not Preference) for Solitude

Dear Dr. Nguyen:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Kirk Warren Brown

Academic Editor

PLOS ONE