A Bibliometric Analysis of Global Scientific Literature on Substance Abuse among School Students Based on PubMed Database (1991-2021)

The purpose of the study was to carry out a bibliometric analysis of the global scientific literature on substance abuse among school children to understand the global research trend on the subject. Bibliographic data of journal articles related to the study topic published during 1991-2021 were retrieved from PubMed database. Data were analyzed using the Bibliometrix R package and MS Excel. The study identified annual growth of publication trends, top authors, leading institutions, Core journals, most contributing countries, and the country collaboration in the research activities on this subject. A total of 3,326 records were selected for the analysis. The annual growth of publications was increasing in trend. Lowry Richard from USA was the most contributing author based on the highest number of publications. The USA was the most productive country publishing the highest number of articles (2408 articles) and the highest international country collaboration with 49 countries all over the world. The University of California was the leading institution (874 articles) in this study.


Introduction
American Psychological Association describes substance use disorder as a "complex condition in which there is uncontrolled use of a substance despite harmful consequences" (Psychiatry.org (n.d.)).Before 2013, there were two separate categories called substance abuse and substance dependence.The Diagnostic and Statistical Manual of Mental Disorders V (DSM-V) published in 2013 removed these two and replaced them with one category called substance use disorders.According to DSM-V-TR (2022), there are ten classes of substances that could lead to substance use disorder which are "alcohol; caffeine; cannabis; hallucinogens; inhalants; opioids; sedatives; hypnotics; stimulants; tobacco and other substances" (American Psychiatric Association, 2022).These substances can cause death both directly and indirectly.Directly, drug overdose could lead to death.Indirectly, substance usage is the underlying main cause of many diseases that lead to death.
In the year 2019, globally there were 583,000 deaths directly and indirectly due to substance use disorders (World Health Organization, 2019).
According to the World Drug Report 2021, globally there were about 275 million people using drugs in the year 2020, and 36 million people were suffering from substance use disorders (United Nations Office on Drugs and Crime (UNODC), 2021).Substance use disorders are not limited to any specific age group.With regard to drug prevalence rates, substance use disorders are three or four times higher among youth than the general population in many countries due to adolescence being the most vulnerable growth period prone to substance use (United Nations, 2001).The main reason for this is the experimental and risky nature of adolescence.
According to the American Addiction Center, 35% of twelfth-grade students used marijuana (National Institute on Drug Abuse (NIDA), (n.d.)).
Among middle school students in the USA, 570,000 were using E-cigarettes in 2018 compared to 60,000 students in 2011, a sharp increase from 0.6% to 4.9% (Cullen et al., 2018).However, the National survey on drug abuse among US students highlighted that there was an unusual decline in substance use in all grades of school students between 2019 and 2021 due to the COVID-19 pandemic effect (Miech et al., 2022).Authorities should give the utmost importance to implementing effective prevention programs for drug abuse in all grades including pre-school (Belcher & Shinitzky, 1998).These programs done in preschool and kindergarten have been shown to reduce cannabis usage by between 7 and 23 percent.A study done on 21-year-old young adults in the USA showed that cannabis usage was lower among the students who participated in kindergarten and preschool preventive programs than the ones who didn't but had a similar background (UNODC, 2015).Policymakers need to consider the research findings to develop an effective plan for these programs.
Bibliometric analysis is a quantitative way of analyzing published scientific literature on a specific subject.It identifies trending subtopics, prominent researchers, productive institutions, most contributing countries, productive information sources that publish research literature, collaborative relationships among countries and researchers, emerging themes, etc.As it provides an overall picture of the scientific production, the analysis guides the researchers to identify gaps in research on a subject and to plan for future research activities.Bibliometric analysis is done on various medical topics to understand the trend in research activities on the specific topic.Some studies would be bibliometric analyses on health informatics (Binkheder et al., 2021(Binkheder et al., ), breast cancer, (Özen Çınar, 2020)), hypertension (Devos & Menard, 2019), income and cardiovascular disease (Ding et al., 2020), and Covid-19 (Chahrour et al., 2020).Some bibliometric studies were carried out related to substance abuse; for example, Bibliometric analysis of substance use disorders in Arab countries (Sweileh et al., 2014); Genetic factors of substance-related disorders (Wang et al., 2021); twenty years analysis on Illicit drug addiction (Khalili et al., 2018); substance use disorder and treatment (Tran et al., 2019); Drug abuse in India; (Azmi & Abbas, 2018); and Publications on Opioids (Azmi & Abbas, 2018).However, based on the knowledge of the author, no bibliometric study was conducted on the specific topic of substance abuse among school children.
As substance abuse among school children is a global threat, it is important to carry out a bibliometric analysis on this topic to identify the research productivity in this area.The analysis will be useful to provide a better understanding to the researchers, policymakers, and other general public about the research trend on substance abuse among school children and to plan for future research activities.

Objective
The study aimed to explore the global trend in the research literature on substance abuse among school children between 1991 and 2021 based on the journal articles indexed in the PubMed database.Specific objectives of the study were to reveal the trend in publication growth, and to identify the prominent researchers, productive countries, leading institutions, and the leading core journals publishing scientific articles pertaining to substance abuse among school children.Further, the study analysed the research collaboration among countries all over the world on this subject.

Methodology
The PubMed database was used to retrieve global research publications related to substance abuse among school children.PubMed is a free biomedical database comprised of more than 30 million citations and abstracts of global publications developed and maintained by the National Center for Biotechnology Information at the US National Library of Medicine (PubMed, 2022).PubMed was chosen because it provides extensive coverage of quality literature in health and life sciences including articles from both established and emerging journals.This comprehensive coverage ensures that researchers have access to a wide range of relevant publications for the analysis.Further, PubMed is freely accessible to researchers worldwide, making it an inclusive and cost-effective resource for conducting bibliometric analysis.
The data collection was done with keyword search to identify all scientific publications related to the study topic during the period between 1991 -2021.The period was considered based on the number of publications indexed in the PubMed database on this study topic and there were many incomplete records available in PubMed before the year 1990.A comprehensive search strategy was developed to retrieve full coverage of the records to achieve the objectives of the study.The entry search terms for the study were selected by consulting several sources without missing important records and avoiding false record retrievals.Medical Subject Headings (MeSH) list established by the National Library of Medicine; USA was referred to get the accurate search terms.Previous studies (Khalili et al., 2018;Sweileh et al., 2014;Tran et al., 2019;Wang et al., 2021 )  Advanced search method was applied and all key search terms related to substance use-related disorders were entered with the 'OR' operator and searched in 'All Fields' (Query 1).Then, query 2 was performed with the search terms "school students" OR "school children" OR "school education".
Query 1 and query 2 were combined with an 'AND' operator.To get only publications related to school students, query 3 was combined with the 'NOT' operator to avoid "university students" OR "college students".As the study was defined during the period from 1991 -2021, the publication date was limited from the 01 st of January 1991 to the 31 st of December 2021.To increase the accuracy of the search results, the publication type was restricted only to journal articles.Table 1 shows the details of the search query.Data were retrieved from the PubMed database on the 15 th of November 2022 and data retrieval was completed on the same day to avoid any discrepancies due to the database updates.
The publications of all languages were included in the study.The absence of duplicate records was confirmed with the support of MS Excel.For this, the retrieved data were exported in CSV format.All the records were retrieved with the abstracts and manually checked one by one to exclude the irrelevant records related to the study topic and the records without required bibliographic information (n=556).Though the publication date was limited to 2021, there were some publications with the publication year 2022, due to the online publications being published in 2021 while the hard copies were being published in 2022.
These records were manually excluded (n=42).Figure 1 shows the selection process of the data.Ethical approval was not required for the study, because it involved only the secondary data.

Figure 1
Flow chart of data retrieval used in the analysis.
Bibliometric analysis was performed using the Bibliometrix R package named 'Biblioshiny' (Aria & Cuccurullo, 2017).The retrieved data (n=3,326) was exported to the R package in PubMed format.MS Excel was also used for the analysis of this study.Figures were developed using MS Excel and R package.Core journals were identified using Bradford's Law (Sudhier, 2010).

Basic information about the data
The total number of records on substance abuse among school students during 1991 -2021 retrieved from the PubMed database based on the selection methods stated was 3,326, which were published in 927 sources.A total of 11,254 authors wrote these articles.Among these, 188 (05.6%) articles were sole-authored publications, and 3,138 (94.3 %) articles were multi-authored publications.On average, the number of co-authors per document was 4.69, which was approximately 5 authors per document.Further, a total of 4,967 author keywords were identified in this analysis.The average age of a document was 12.1 years and the annual growth rate of articles was 4.97%.

Figure 2
Growth of global research publications on substance abuse among school students from 1991 to 2021.

Contribution of prominent authors
The top twenty prominent authors related to substance abuse among school children were selected based on the number of articles published during the study period.As PubMed doesn't provide the number of citations, Prominent authors were selected based on the number of publications.Lowry Richard from USA was the prominent author contributing the greatest number of publications (n= 40) related to the study topic.It was followed by Kann Laura (n=37) from USA; Sussman Steve (n=31) from USA.Among the top twenty, 12 authors were from USA (

Figure 3
Publication growth of top ten authors in three time periods.

Productive country
Analysis of the research contribution of countries on substance abuse among school children was carried out based on the number of articles published during the study period.Publications retrieved from PubMed database with at least one author's affiliation mentioned were considered for the analysis.The study indicated an increasing trend in the involvement of research activities on this subject field by researchers from China.

Productive sources
Core journals on substance abuse among school students were identified based on Bradford's Law.According to Bradford's law, the sources are classified into three zones as zone 1, zone 2, and zone 3. Bradford's Law is used to identify the core journals in a particular subject area categorized in zone 1; nuclear zone (Zhang et al., 2022).  5.

Table 5
Ranked list of core journals publishing more articles.The USA had the greatest number of research in 49 countries all over the world.It was followed by Canada, Italy, Australia, and Germany with 24, 21, 19, and 15 countries respectively.Twenty-six countries had collaborated with less than five countries on substance abuse among school children; Seven countries had collaborated with five to ten countries, while another seven countries had collaborated with more than ten countries.

Discussion
Substance abuse among schoolchildren is a common problem in many related to substance use disorders were also used to select the relevant search terms.The list of search terms was finalized through a discussion with a senior medical librarian, who is an expert in searching PubMed database.Though we use specific search terms to retrieve the data, PubMed automatically adds all relevant MeSH terms to the search[PubMed, 2022.].

Figure 2
Figure 2 illustrates the overall trend in the growth of global research publications on substance abuse among school students over the years during the study period.The annual growth of research publications was increasing in trend over the years, though there were small fluctuations in growth.There

Figure 3
Figure3illustrates the analysis of the publication growth of the top ten authors categorized in three time periods.Among the top ten authors, Lowry R, Kann L, Sussman S, Wada K, and Flisher AJ had been working in this research area constantly throughout the study period.Fifth-ranked author were analyzed and the top 20 institutions were ranked for each period.The University of California was the leading institution during the periods 1991-2000(60 articles) and 2011-2021(649 articles), whereas the Division of Adolescent and School Health was the leading institution during the years 2001-2010 with 188 publications.
Zone I has the top 25 core journals, which published research articles on substance abuse among school children.The study identified 25 most productive journals among a total of 927 journals.The top 25 journals published a total of 1,114 articles among the total of 3,326 articles.'Addictive behaviors' was found to be the top leading journal publishing the highest number of articles (n=118) on substance abuse among school children.The ranked list of top ten journals based on the number of publications is displayed in Table

Figure 4
Figure 4 illustrates the research collaboration on the study topic among various countries during the period 1991 -2021.The relationship between the two countries was analysed if the two countries had at least one research collaboration.The intensity of the blue color reflects the amount of research collaboration.The higher the intensity of the blue color, the higher the frequency of research collaboration.
countries.Bibliometric analysis of 3,326 articles retrieved from PubMed database on substance abuse among school children during the period 1991 -Conclusion Bibliometric study on the global scientific literature on substance abuse among school children highlighted important facts of research trends in this field during 1991-2021.The study concluded that the USA was the most dominating country, contributing research on topic.The study identified the prominent authors, institutions, productive information sources, and international country collaboration.The findings of the study are useful to guide the research community involved in research activities related to the field of substance abuse among school children.As substance abuse among school children creates serious threats in society, researchers should play a key role in promoting more research activities in this subspeciality to prevent school children from substance abuse.

Table 1
Details of the search query Table 2).It is highlighted that Karl Peltzer from South Africa was included among the top twenty authors who published The study revealed that among the total of 11,254 authors, a major proportion (97.7%) of authors (10,991 authors) wrote less than 5 articles each.
Table 3 provides the rank list of the top twelve productive countries.USA was the most productive country with the highest number of country with 188 publications during 2001-2010; it was ranked as the 2 nd most productive country next to USA with 2,730 publications during 2011-2021.

Table 3
Ranked list of top 10 countriesIt was followed by the Division of Adolescent and School Health (n= 714); then the University of Southern California with 680 publications.Except for the sixth-ranked University of Auckland from New Zealand, all other institutions among the top ten were from USA.