Characteristics of Publications on Occupational Stress: Contributions and Trends

This study aimed to analyze the bibliometric characteristics of the publications on occupational stress and highlight key research topics and future trends. The Web of Science Core Collection database was searched to collect publications on occupational stress, from inception to December 9, 2020. Two authors independently screened eligible literature and extracted the data. Bibliometric analyses were performed using VOSviewer 1.6.6 and R 3.6.3 software. Overall, 6,564 publications on occupational stress were included. “Stress,” with a total link strength of 1,252, appeared as the most co-occurrence keyword, followed by “occupational stress,” “job stress,” and “job satisfaction.” All studies were published between 1956 and 2020. Among them, 6,176 (94.35%) papers were written in English, and 4,706 (70.25%) were original articles. The top three Web of Science categories were “public environmental occupational health” (n = 1,711), “psychology, applied” (n = 846), and “psychology, multidisciplinary” (n = 650). The 100 top-cited articles were mentioned a total of 36,145 times, with a median of 361, ranging from 174 to 5,574. The United States was the most productive country, with 1,780 publications. The main partners of the United States were England and China. Three themes of occupational stress research were identified: job satisfaction, burnout, and occupational stress-related health problems. This bibliometric analysis provides a comprehensive understanding of the trends and most influential contributions to the field of occupational stress, thus promoting ideas for future research.


INTRODUCTION
Occupational stress is the process by which workplace psychological experiences and demands (stressors) produce both short-and long-term changes (strains) in mental and physical health (1). The annual National Health Service (NHS) staff survey conducted in England showed that approximately 30% of workers suffer from occupational stress (2). Moreover, a meta-analysis found that the overall prevalence of occupational stress among nurses working in Iranian hospitals was 60% (3). Occupational stress is associated with many diseases (1), such as cardiovascular diseases (4,5), depression (6), and type 2 diabetes (7). Occupational stress is also closely related to insomnia (8), alcoholism (9), smoking (10), and unhealthy weight fluctuations (11), which further affect physical and mental health.
Recently, increasing research has focused on occupational stress. Bibliometric analysis can detect critical junctures in the development of research fields, especially intellectual turning points and pivotal moments (12). Moreover, it can provide insights regarding prominent areas of interest, with an emphasis on the countries, institutions, journals, and authors with the greatest global impact. The scientific knowledge graph is a new domain in the development of bibliometric analysis, which can visually represent research results (13,14). Another crucial component of bibliometric analysis is citation analysis, which provides comprehensive information regarding cited articles (15). Bibliometric analysis has been applied in various disciplines, such as neuropsychology (16), cancer (17), respiratory medicine (18), , and vaccines (20).
However, no bibliometric analysis of publications has been conducted on occupational stress. Since occupational stress has become an important area of occupational health, and increasing research has been published on the topic, it is imperative to conduct a bibliometric analysis in this area. Therefore, in the present study, we aimed to provide a broad understanding of occupational stress and to highlight the key research topics, thus promoting ideas for future studies.

Search Strategy
The Web of Science Core Collection database was searched for publications on occupational stress from inception to December 9, 2020. The search strategies were as follows: [occupational OR job OR job-related OR (job related) OR work-related OR (work related) OR workplace OR (work place) OR professional] AND (stress * OR strain * ) in the title. The language and literature types were not limited during the process of retrieval. Literatures were excluded on several criteria. First, the title of these literatures had the above-mentioned keywords; however, the content of the literature was about heat stress, muscle strain, oxidative stress, stress fracture, postural stresses, non-work-related posttraumatic stress, work-related physical stress, occupational ergonomics, and mechanical stress in the workplace or occupational groups. In this occupational stress literature bibliometric analysis, environmental stressors refer to psychosocial stressors. Second, literatures were excluded when psychological stress was not work related or occurring in nonworking people, such as students or full-time mothers. Finally, items were excluded when strain referred to a microorganism in the workplace. Two authors independently screened titles, abstracts, and full texts for eligible literature. Disagreements were resolved through discussion or by a third reviewer.

Data Extraction
Information including the title, publication year, language, author, journal name, affiliation, keywords, document type, Web of Science category, abstract, and total number of citations were identified and recorded by two authors. The results were compared, and disagreements were resolved through discussion or by a third reviewer.

Statistical Analysis
We used VOSviewer software (version 1.6.6) to analyze the co-authorship, co-occurrence, co-citation, citation, themes, and topics. We also used R software (version 3.6.3) to perform correlation analysis, which was used to evaluate the relationships between the different terms. A p-value of ≤ 0.05 (two-tailed) was considered statistically significant.
The top 10 most published journals, countries, organizations, and authors for occupational stress are shown in Figure 2. In total, 1,003 (14.82%) papers were published in the top 10 active journals. The International Journal of Psychology had the most publications, with an impact factor of 1.255 in 2019. Work and Stress ranked second, with an impact factor of 3.512, and ranked in Q1 for the psychology applied category in 2019. A total of 5,618 institutions from 125 countries contributed to the publications on occupational stress. The most productive author was Cooper CL from the University of Manchester, with 91 related papers.

Bibliometric Analysis of Keywords
Keywords occurring over 10 times in the database were included in the analysis. Of the 6,818 keywords, 222 met the threshold. "Stress" (with a total link strength of 1 252) appeared as the FIGURE 3 | Bibliometric analysis of co-occurrence of keywords in publications of occupational stress. The size of nodes indicates the frequency of occurrence. The curves between the nodes represents their co-occurrence in the same publication. The shorter the distance between two nodes, the larger the number of co-occurrence of the two keywords. most co-occurring keyword, followed by "occupational stress, " "job stress, " and "job satisfaction" (Figure 3).

Bibliometric Analysis of the 100 Top-Cited Papers
The Supplementary Material shows the 100 top-cited papers in the field of occupational stress. The 100 top-cited papers were cited 36,145 times in total, ranging from 174 to 5,574, with a median of 361. The average number of citations per year ranged from 3 to 136, with a median of 18 mentions for the 100 top-cited papers. The total number of citations of the 100 top-cited papers were correlated with the annual mean citations (r = 0.791, p < 0.001). Of the 100 top-cited publications, 93 were original articles, and seven were reviews ( Table 1)

Bibliometric Analysis of Co-authorship
The co-authorship maps of organizations and countries are shown in   also enrolled into analysis. Of the 38,928 sources, 459 met the threshold. Four clusters of the cited sources were obtained via bibliometric analysis. The Journal of Applied Psychology, Work and Stress, and the Journal of Organizational Behavior ranked in the top three, with 5,760, 2,749, and 2,159 citations, respectively ( Figure 5B).

Bibliometric Analysis of Themes and Trends
Terms from the title and abstract fields were extracted. Three themes of occupational stress research were identified: job satisfaction, burnout, and occupational stress-related health problems. Indicators display the current publications from purple to yellow. More researches focusing on stress-related health problems and stress intervention have been published recently (Figure 6).

DISCUSSION
Bibliometric analysis has been firmly established as a scientific specialty and is an integral component of research evaluation methodology, especially within the scientific and applied  fields (21). With the proliferation of medical information, bibliometric analysis has been used to examine various health research domains (22). However, no bibliometric analyses have been conducted among publications on occupational stress. Therefore, this study aimed to provide a comprehensive analysis of published literature in the field of occupational stress. In this study, we found that the number of literatures published on occupational stress have increased between 1956 and 2020. Occupational stress drastically increased during COVID-19 pandemic, requiring comfort rules for healthcare workers after use of protective device to improve work performance reduction, difficulty in concentrating, and sleep disorders (23). People have begun to emphasize mental health and have realized that occupational stress adversely affects both work performance and overall health (1,24). Therefore, researchers have increasingly focused on occupational stress. "Stress" appeared as the most co-occurring keyword, followed by "occupational stress, " "job stress, " and "job satisfaction." Studies concentrated on the following aspects: the theoretical model of occupational stress (1), the stress levels of different occupational groups (25,26), the relationship between occupational stress and job satisfaction (27), the relationship between occupational stress and disease (1), biomarkers of occupational stress (28), and the relationship between occupational stress and behavioral changes (9). Occupational stress is an interdisciplinary science of public health and psychology. Thus, the top three Web of Science categories were: "public environmental occupational health, " "psychology, applied, " and "psychology, multidisciplinary." The most frequently cited article received 5,574 citations and was published in 1979 (29). The major findings of the study indicated that redesigning work processes to allow a greater decision latitude for a broad range of workers could reduce mental strain. This can be achieved without affecting the job demands associated with organizational output levels. The results of the study were widely utilized in subsequent research. Combined with the passage of time, the study had the highest frequency of citations. Meanwhile, the study (29) appeared as the most co-cited reference. FIGURE 6 | A term co-occurrence map according to terms from the title and abstract fields. Indicators show the current publications from purple to yellow. The size of the frames represents the frequency of appearance as the keywords. The distance between the two frames indicates their correlation. The closer the distance, the more similar the theme.
The 100 top-cited studies were not recent, having been published between 1958 and 2015. Similar findings were reported in previous studies (16,20). It is difficult to obtain high total citations for newly published articles due to the short duration of their availability. Among the 100 top-cited articles, the Journal of Applied Psychology had the highest number of publications, followed by the Journal of Organizational Behavior. These are two classic journals in the applied psychology field, ranking in the top 10%. While studies on occupational stress have been conducted worldwide, developed countries perform better than developing countries in this research area. The United States was the most productive country with highest average citation. The pronounced influence of the United States may be attributed to its large number of scientific research institutions and abundant research funds. They pay attention to occupational stress earlier and mental health. Major partners of the United States were England and China. Although China ranked third among the most-productive countries, it did not appear among the 100 top-cited articles. This phenomenon indicates that developing countries may disregard occupational stress in favor of devoting more energy to solving physical health problems.
Three themes of occupational stress research were identified: job satisfaction, burnout, and occupational stress-related health problems. Presently, most studies have a cross-sectional design, and few longitudinal studies or pilot trials have been conducted to evaluate health effects and interventions (30,31). In addition, occupational stress measurement tools are diverse, and the results are difficult to compare. Therefore, more high-quality studies with improved designs focusing on the measurement of occupational stress are needed in the future. More research focusing on stress-related health problems and stress intervention has been published recently. The long-term health effects of occupational stress require more well-designed cohort studies to verify. Furthermore, field intervention trials are needed to evaluate the effects of different occupational stress interventions.
There are some limitations to this study. First, we may have missed literatures that did not contain the keywords in the title. Second, only the Web of Science database was searched for analyses, and we did not collect data from other databases such as Embase, Medline, Scopus, and Google Scholar. Third, the number of citations of each publication will change over time; subsequently, the 100 top-cited articles will also change. Thus, our research is only representative of the current research context. In future studies, we will include more databases in the analyses and dynamically track the changes in this field. Despite these limitations, we believe that as the first bibliometric analysis of occupational stress, our findings make a significant contribution to understanding the trends and influential publications in this domain.
In conclusion, this study analyzed the publications on occupational stress according to the authors, journal, publication year, country, institution, and study type. Moreover, this study provides insight into the 100 top-cited publications in occupational stress research. This bibliometric analysis offers a more comprehensive understanding of trends and the most influential contributions to the field of occupational stress, thus promoting ideas for future research.

DATA AVAILABILITY STATEMENT
The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding authors.

AUTHOR CONTRIBUTIONS
YoZ and YaZ designed the study. YaZ and LH analyzed the data. YaZ drafted the manuscript. LH, YW, YL, and YoZ edited the manuscript. All authors contributed to the article and approved the submitted version.

FUNDING
This study was supported by the National Nature Science Foundation of China (No. 82073521).