Mapping Research Trends of Universal Health Coverage From 1990 to 2019: Bibliometric Analysis

Background: Universal health coverage (UHC) is one of many ambitious, health-related, sustainable development goals. Sharing various experiences of achieving UHC, in terms of challenges, pitfalls, and future prospects, can help policy and decision-makers reduce the likelihood of committing errors. As such, scholarly articles and technical reports are of paramount importance in shedding light on the determinants that make it possible to achieve UHC. Objective: The purpose of this study is to conduct a comprehensive analysis of UHC-related scientific literature from 1990 to 2019. Methods: We carried out a bibliometric analysis of papers related to UHC published from January 1990 to September 2019 and indexed in Scopus via VOSviewer (version 1.6.13; CWTS). Relevant information was extracted: the number of papers published, the 20 authors with the highest number of publications in the field of UHC, the 20 journals with the highest number of publications related to UHC, the 20 most active funding sources for UHC-related research, the 20 institutes and research centers that have produced the highest number of UHC-related research papers, the 20 countries that contributed the most to the research field of UHC, the 20 most cited papers, and the latest available impact factors of journals in 2018 that included the UHC-related items under investigation. Results: In our analysis, 7224 articles were included. The publication trend was increasing, showing high interest in the scientific community. Most researchers were from the United States, the United Kingdom, and Canada, with Thailand being a notable exception. The Lancet accounted for 3.95% of published UHC-related research. Among the top 20 funding sources, the World Health Organization (WHO), the Bill and Melinda Gates Foundation, and the National Institutes of Health (NIH) accounted for 1.41%, 1.34%, and 1.02% of published UHC-related research, respectively. The highest number of citations was found for articles published in The Lancet, the American Journal of Psychiatry, and the Journal of the American Medical Association (JAMA). The top keywords were “health insurance,” “insurance,” “healthcare policy,” “healthcare delivery,” “economics,” “priority,” “healthcare cost,” “organization and management,” “health services accessibility,” “reform,” “public health,” and “health policy.” Conclusions: The findings of our study showed an increasing scholarly interest in UHC and related issues. However, most research concentrated in middleand high-income regions and countries. Therefore, research in low-income countries should be JMIR Public Health Surveill 2021 | vol. 7 | iss. 1 | e24569 | p. 1 http://publichealth.jmir.org/2021/1/e24569/ (page number not for citation purposes) Ghanbari et al JMIR PUBLIC HEALTH AND SURVEILLANCE


Introduction
Universal health coverage (UHC) was one of the ambitious, health-related "sustainable development goals" (SDGs) set by the United Nations (UN) General Assembly in 2015, and is one of the top priorities of their 2030 agenda.UHC represents the hope for better health for the world's poorest [1][2][3].The World Health Organization (WHO) has defined UHC as a policy for "ensuring that all people can use the promotive, preventive, curative, rehabilitative and palliative health services they need, of sufficient quality to be effective, while also ensuring that the use of these services does not expose the user to financial hardship" [4].
At least half of the world's population does not have access to full coverage for a package of essential health services [5].Health expenses lead more than 100 million people worldwide to extreme poverty every year, often forcing people to make intolerably difficult choices between purchasing food for their children and families, paying for child education, or paying for vital health services [2,6].
Countries differ in the way they address UHC provision based on a wide range of factors, such as political, economic, social, epidemiological, and technical considerations [7,8].The path to UHC involves important policy choices and inevitable trade-offs [9].The extent of the impact of a successful UHC implementation is referred to as the "Third Global Health Transition" [10].Sharing various experiences of achieving UHC, in terms of challenges, pitfalls, and future prospects, can help policy and decision-makers benefit from global good practices and reduce the likelihood of committing errors and wasting resources better allocated elsewhere.As such, scholarly articles and technical reports are of paramount importance in shedding light on the determinants that make UHC achievement possible [11,12].Nearly all of the Organization for Economic Co-operation and Development (OECD) countries and emerging economies, such as Brazil, China, Colombia, Costa Rica, India, Indonesia, and Russia, have achieved UHC [13].These countries' experiences can be a major source of evidence of why UHC is desirable and how it should be achieved.Evidence shows a strong relationship between life expectancy at birth and UHC indicators, reflecting the 3 core dimensions of universal health coverage [14].In moving to UHC, some countries such as Ghana, Indonesia, and Vietnam have increased their UHC indices over time, 1.43%, 1.85%, and 2.26%, respectively, mostly by improving both financial protection and service coverage [15,16].
In recent years, researchers have been using scientometrics, a branch of information science and a subfield of bibliometrics, to quantitatively investigate emerging research patterns in the scientific literature [17].In addition, scientometrics enables an assessment of trends in article citations and how these indicators and measurements can impact policy and management.Using scholarly databases and visualization technology allows researchers to gain a good understanding of the publication trends related to a given topic [18,19].
To the best of our knowledge, there is a dearth of information concerning research patterns in the field of health care management and, specifically, UHC.Therefore, the purpose of this study is to conduct a comprehensive analysis of UHC-related scientific literature from 1990 to 2019.

Ethics Approval and Consent to Participate
This study was waived from ethical approval because it did not include data on animals or human subjects, and it was based on publicly available data.

Data Sources
This quantitative study was based on medical informatics, data and text mining, and scientometrics techniques [20].Independently, 2 authors searched Scopus from January 1, 1990, to September 24, 2019.Disagreements between them were resolved through discussion until consensus was reached.

Inclusion and Exclusion Criteria
We limited our search to only scholarly items dealing with UHC, using "universal health coverage" as the keyword.The search was performed without language restrictions.All records relevant to the field of UHC were deemed eligible and, as such, retained in our investigation.

Data Extraction
Data were downloaded in comma-separated values (CSV) format.Independently, 2 authors extracted relevant data, namely, (1) the number of documents published within the study period, (2) the 20 authors with the highest number of publications in the field of UHC, (3) the 20 journals with the highest number of publications related to UHC, (4) the 20 most active funding sources for UHC-related research, (5) the 20 institutes and research centers that have produced the highest number of UHC-related research papers, (6) the 20 countries that contributed the most to the research field of UHC, (7) the 20 most highly cited papers, and (8) the latest available impact factor of journals in 2018 that included the UHC-related items under investigation.Any disagreements between the 2 authors were resolved through discussion until consensus was reached.

Data Analysis
Ad hoc visualization software was used to visualize UHC-related research hotspots, patterns, directions of research development, and other relevant trends, using networks and graphs.All data were imported and loaded into VOSviewer (version 1.6.13;CWTS).For visualization publication density worldwide (ie, publication trends among countries), the open-source tool GunnMap was used [21].

Results
After searching Scopus, a pool of 7224 records was included in our analysis.The increasing publication trend related to UHC from January 1990 to September 2019 is shown in Table 1.
The 20 authors with the highest number of publications in the field of UHC are listed in Table 2. Of the 20 authors, 4 are from the United States, 4 are from the United Kingdom, and 3 are from Thailand.
The network distribution of authors publishing in the field of UHC is shown in Figure 1.The 20 journals with the highest number of publications related to UHC are listed in Table 3.The Lancet accounted for 3.95% of published UHC-related research.
Table 1.Number of publications related to universal health coverage per year, as indexed in Scopus.Table 4 shows the 20 most active funding sources for UHC-related research.Among them, the WHO, the Bill and Melinda Gates Foundation, and the National Institutes of Health (NIH) accounted for 1.41%, 1.34%, and 1.02% of published UHC-related research, respectively.Table 5 lists the 20 institutes and research centers that have produced the highest number of UHC-related research papers.

Number of publications Year
Table 6 shows the countries that contributed the most to the research field of UHC.Among them, the United States, the United Kingdom, and Canada contributed 2426, 919, and 545 papers, respectively.
Figure 2 shows the density distribution of UHC-related publications among different countries and regions around the world.
The 20 most highly cited papers are listed in Table 7.The highest number of citations was found for papers published in The Lancet, the American Journal of Psychiatry, and the Journal of the American Medical Association (JAMA).

Principal Findings
This study quantitatively assessed the publication trend related to UHC over the past 19 years.UHC-related publications have been on the rise in recent years, and this seems to be the major focus of researchers, given the important role that UHC can play in improving equity in access to health services and provisions.UHC can enable important achievements in the health sector worldwide.The growth of health-related scientific publications in the field of policy and management, and especially UHC, reflects the global interest and participation of different stakeholders, including researchers, in identifying the different dimensions and determinants that can make it possible to achieve UHC.
Undoubtedly, relying on scholarly publications can improve the performance of the health sector to achieve UHC-related goals.The rigor of the scientific method, if properly followed, can lead to fundamental changes in all areas of life, including health.Bibliometrics-based literature reviews can play an important role in examining the process of scientific publications and orienting researchers in this field [22].
From 1990 to 2019, scholarly publications in the field of UHC have been gradually increasing, especially after 2015 when policy and decision-makers have given particular emphasis to achieving UHC as one of the SDGs.Political commitment and support on this issue has contributed to the prioritization of UHC and put it on the policy and research agenda [23].
This investigation shows that authors from the United States, the United Kingdom, Canada, and Thailand produced the highest number of publications related to UHC.Scientists from the United States, the United Kingdom, and Canada have done research on the possible ways to achieve UHC goals in collaboration with various stakeholders, including health care policy and decision-makers.Thailand is one of the countries working hard to improve its health sector by making profound reforms.Since 2002, despite economic-financial problems and political instability, proper support for UHC has provided Thai citizens with a good level of health services and provisions.Therefore, researchers in this country have tried to disseminate their experiences and practices in the field of UHC to other countries around the world [24].
Usually, researchers aim to have their scientific findings published in prestigious journals so that their papers can have the highest exposure in terms of impact and receive adequate attention and citations from other researchers [25].The Lancet, which has a high impact factor and plays an important role in influencing and shaping future scientific research, has published the highest number of articles related to UHC.Also, journals in the fields of health care policymaking, decision-making, and management have attracted authors' interest in submitting papers.UHC is a major topic because of its impact on all aspects of health [26].
The WHO, the London School of Hygiene and Tropical Medicine, and the Harvard School of Public Health were among the institutions and research centers that played a major role in supporting UHC-related research.The WHO's institutional nature makes it naturally interested in topics such as UHC, as XSL • FO RenderX it strives to provide the best evidence for a given health-related issue.The London School of Hygiene and Tropical Medicine is also one of the most prestigious institutions that, in recent decades, has promoted UHC-related studies, especially in lower-income countries, to improve health in these countries and achieve UHC goals.It strives to empower researchers in the field of health and provide high-quality public health education, as does Harvard School of Public Health.
It is important to note that, in the last decades, these two institutions have become prominent in the fields of health policy and management, indicating that they play an important role in developing UHC-related issues.

Limitations
Despite strengths such as methodological rigor, transparency, and reproducibility, this study has some limitations that should be properly recognized.Its major limitation is the use of a single bibliographic database (Scopus).As such, results should be replicated utilizing other major scholarly databases like PubMed/MEDLINE or Web of Science.

Conclusion
The findings of our study showed an increasing scholarly interest in UHC and related issues.However, most researchers were from the United States, the United Kingdom, and Canada, with Thailand being a notable exception.Research in low-income countries should be promoted and supported, as this could enable a better understanding of the determinants of the barriers and obstacles to UHC achievement and improve global health.

Figure 1 .
Figure 1.The distribution of authors publishing research in the field of universal health coverage.

Figure 2 .Table 7 .Figure 3 .
Figure 2. Density of publications related to the research field of universal health coverage worldwide.

Table 2 .
Authors with the highest number of manuscripts related to universal health coverage.

Table 3 .
Journals with the highest number of articles related to universal health coverage.
a -not available.

Table 4 .
Most active funding sources for universal health coverage (UHC)-related research.

Table 5 .
Highest producing institutes and research centers for universal health coverage research.

Table 6 .
Countries and regions that contributed the most to the research field of universal health coverage (UHC) during 1990-2019.