Developing Status and Hotspot Analysis of Health Policy With Bibliometrics Methods: 2011-2020

Objectives: This study mainly discusses the developing status in the eld of health policy in recent two decades to provide an effective reference for researchers. Methods: Health policy publications published in Web of Science between 2011 to 2020 were searched, screened, organized, and analyzed the yearly-outputs, research author, institution, regional distribution, keywords, subject categories, and so on. Results: The total number of publications in health policy has shown a trend of upward in the past twenty years. Health policy was identied as the most productive journal. The research of United States takes the lead in this eld. Health care, public health, epidemiology, children, and quality of life will likely to take a dominant position in future research. Conclusion: The eld of health policy has developed a stable research community with good partnerships, and the high-impact authors lead the development of the discipline. The hotspots of health policy research are constantly updated with the trend of social development and have strong timeliness. With constantly study, health policy has become a relatively mature research topic, but it doesn't mean the termination of the study. It remains to be properly explored and improved to protect people’s health and promote the quality of life in the future. Editorial Material (956, 7.77%), Meeting Abstract (745, 6.06%), Proceedings Paper (109, 0.89%). The data indicate Article and Review made up the major types of documents related to health policy, which accorded with the distribution of reference types characteristics in bibliometric research (Zhi & Ji, 2012). For been 40 used in the 11 632 among which for by 9 953 articles (197, (110, 0.82%). indicates that It may


Introduction
Health policy refers to decisions, plans, and actions that are undertaken to achieve speci c health care goals within a society according to World Health Organization. The speci c health policy can determine a nice vision for the future, and then in turn help to con rm objectives and reference points for the short and medium-term. Health policy is guided by beliefs and values about humans and health (Alligood & Miles, 2011). It summarizes matters of priority and the prospective roles of different organizations, establishes consensus and informs people. Health policy is the sum of miscellaneous tools aimed at dealing with speci c public health issues and achieving de nite health work goals (Willson, 2020). The importance of strengthening the improvement and establishment in health policy research has been increasingly emphasized. It performs important social functions, such as developing academic medicine, adjusting the allocation of health resources, coordinating the interests of relevant groups, and driving social development. Countries around the world accept that health is a basic human right, de ne the purpose of medicine as the maintenance of health (Hart, Larson, & Lishner, 2005). Therefore, the formulation of health policies in various countries revolves around the goal of improving health and regard increased equity and access to health as a fundamental starting point (Davis & Howden-Chapman, 1996). The formulation and implementation of health policies cannot be accomplished in a short period (Flisher et al., 2007) which needs extensive publicity campaigns, persuasion, and education to achieve the goal.
Bibliometrics was rst proposed by Pritchard (Hong, He, Nguyen, Liu, & Zhuang, 2013). Bibliometrics is an applied science that systematically contributes to appraising the importance and status of scienti c publications in a designated eld (Huang et al., 2016). As an applied tool, it can evaluate the contribution of the scienti c productions to the development of research within a speci c country, region, or topic (Yang, Zhou, & Wang, 2013) and be widely used to explore current research trends. It provides a research method for the geographical distribution, topic evolution, hot trends, and so on of a particular domain (Chiu & Ho, 2007; W.GLANZEL, A.SCHUBERT, & H.-J. CZERWON, 1999). It has been used to evaluate the scienti c outputs, study patterns of institutions, journals, authors, and territories or research trends and hotspots. In the past several years, bibliometrics has been applied to document statistics in different elds.
The study would provide bibliometric analysis and research trends with substantive discussion in health policy research between 2011 and 2020. The goals of this study are: (1) summarizing publication patterns for institutions, subject categories, and countries in health policy; (2) assessing research performance of author, institution, nation, and journal from diversiform angles; (3) generalizing research areas, global research trends and hot issues to serve as a signi cative reference for relevant researches.
The study structure is as follows: Materials and methods section describes the whole process of research design, covering data sources, retrieval strategies, cleaning criteria, and relevant analysis. The result and discussion section shows the evaluation conclusion and provoking thoughts. The last section summarizes the main conclusion and the limitations of this study.

Materials And Methods
Data source and search strategy Web of Science (WOS), as a signi cant database for access to global academic information, contains more than 18 000 authoritative and in uential journals. This database covers multidisciplinary research elds, which divides articles into 256 subject categories. Catalog searching, keywords searching and code searching are the most general searching approaches. This study selected Web of Science as the data source. Under the guidance of experts in related elds, two research workers independently search for documents based on the subject term: health policy.

Inclusion criteria and exclusion criteria
A series of inclusion criteria and exclusion criteria related to the topic, category, content, and period are established to guide publication retrieval and screening. The inclusion criteria the study implemented were as follows:(1) Productions in the eld of health policy research; (2) being published between 1st January 2011 and 31 December 2020; (3) database is con ned to WOS. The exclusion criteria were the following: (1) repetitive research articles; (2) paper information is required; (3) article needed manual searches; (4) some corrections le. Figure 1 shows the whole process that we identify and screen the publications in this study.

Data analysis
In this study, 11 632 selected publications were imported and analyzed with some professional document analysis software, such as CiteSpace Vos Viewer. Relevant publications were analyzed according to the following indicators: (1) publications quantity and overall change trend; (2) language of publications; (3) The most productive institution, country and author; (4) references with high citation and visualization analysis; (5) research hotspot.

Results
In this study, this study used bibliometrics analysis and visualization approach to analyze the number and quality of published articles about health policy. The results were presented in the form of designed charts and visual maps.

Yearly research publications
To some extent, the chart about the annual distribution trend of publication quantity can reveal the research status in a certain eld. During the retrieval process, we nd the number of publications didn't show a relatively stable trend before 2011, which can't meet the requirements of bibliometrics research. This phenomenon may be related to the values of giving priority to economy in the world, especially in the developing countries. From 2011 to 2020, the total number of 11 632 publication articles was indexed in the database. It can be indicated from Fig. 2 that the annual number of publications has reached a plateau overall and shown an upward trend from 2011 to 2020. We found there was a high correlation between the annual cumulative number of publications and year [correlation coe cient(R 2 ) = 0.994]. The tted curve was (Y is the annual cumulative number of publications, x is the publication year) which can predict the future trend of publication numbers. Therefore, it can be assumed that the research and application of health policy are arising in the world and the number of articles related to this eld will maintain stable uptrend in the future. The researchers believe that after the outbreak of COVID-19, the world and research institutes will pay more attention to the study of health policy to protect people's right to health and promote the further development of the discipline.
Languages and types of publication countries/territories with the largest number of publications, there is one South American country, one Oceania country, one Asia country, two South American countries and ve European countries. Figure 3 shows the global distribution of countries' published articles. We can conclude that Europe and North America are leaders in this eld, especially in Europe. It is probably because Europe's medical technology and level are in the leading position around the world. countries/territories with the largest number of publications, there is one South American country, one Oceania country, one Asia country, two South American countries and ve European countries. Figure 3 shows the global distribution of countries' published articles. We can conclude that Europe and North America are leaders in this eld, especially in Europe. It is probably because Europe's medical technology and level are in the leading position around the world.

Most productive journals
The research found that 1 786 journals had published articles in the eld of health policy from 2011 to 2020. Table 1 shows the top ten productive journals which had been publishing 13.437% of 11 632 articles. The journal with the most outputs was "Health Policy" comprising 308 (2.506%) articles. The following four journals were European Respiratory Journal (303, 2.469%), BMC Health Services Research (273, 2.221%), Plos One (229, 1.863%), Social Science Medicine (224, 1.827%). Double graph overlay for journals can exhibition distribution and citation trajectory of publications in different subjects from which researchers can have a general idea of basic foundations and application elds. Figure 4 covers two reference paths that indicated the relationship between journals of citing articles and journals of references. In the main body of Fig. 4 the width of the line represented citation strength between two different disciplines. The width of the ellipse stands up the number of authors and the height of the ellipse shows the number of publications. It can be indicated that the citing articles in the eld of health policy concentrated on Medical and Clinical, and Education and Health. The main references belonged to Molecular and Biology, Nursing and Medicine.     Figure 5 shows the high-cited Articles and document co-citation network.   Hotspot keywords analysis Foam Tree was generated by Carrit2, which is an open search-based clustering engine. This study chose "Lingo" as the clustering algorithm and got Fig. 7. The size of the polygon represents the frequency of different topics. As Fig. 7 shown, Evidence Review was the most common research approach in this eld.
Changes in health policy and disease policy have aroused researchers' wide concern.
The keywords of articles are phrases or words extracted from the body, title, or abstract that can reveal the theme of the scienti c papers. The research method of keywords was rst used by Chiu and Ho for bibliometrics research to nd a sally port for study trends and development (Sorensen & Aaron, 2009). Figure 8 shows the result of the keyword co-appearance network, in which the size of keywords represents its word frequency. The research adopted the word frequency analysis to extract the core content of the publications and study the hotspots in this eld. Figure 8 shows the top 10 keywords ranked by the word frequency. Except search word ('health policy'), the ve most frequently appeared and available keywords were Health Care, Public Health, Epidemiology, Children and Quality of life. We can certainly deduce that the research focuses on Health Care Sciences & Services, Public health, Disease prevention, Epidemic prevention, and cure in the recent 10 years. Speci c hot keywords are analyzed as follows: Public health As a contrast to traditional medicine, public health focuses on population health rather than individual patients. Public health is a social service aiming to promote entire health situation and prevent diseases. (Ng & Ruger, 2014) Of course, it also involves the work of demographic surveillance, food hygiene security etc. public health law and public health policy help people reduce health risks, prevent disease, and striving for healthy populations, which are the most fundamental guarantee. (Allan, 2017) Public health policy is usually designated by government departments that represent the medical service goals in a nation. Public health policy has been regarded as the most available approach to reduce public health harms. For example, the Alcohol Harm Reduction Strategy for England acquired great accomplishments in decreasing tra c accidents and public security affairs due to alcohol abuse. (Braillon & Dubois, 2005) Public health policy adjusts the service orientation with the trends of health indicators to satisfy the health needs of the population. ( with high mortality (such as coronary-heart-disease, renal disease, etc.). 3.pay more attention to the special crowd (such as pregnant women, elderly people, etc.).

Health care
Health care always consists of public and private institutions and insurance programs. (None, 1993) Health care is closely correlated with pharmaceutical and healthcare elds, which work to regulate the medical services, preserve the population's health, make basic medical and health services more equitable and accessible and eventually maintain social stability. Health care policy is always considered as decisions, plans and actions adopted to reach speci c goals within the society.(Dimick, J., Ryan, & A., 2014) Health care policy covers several issues related to health, covering the nancing of health care, preventive medicine, chronic diseases and disabilities, mental health and long-term care ,etc. Establishing an effective health care policy has become a worldwide problem, which is concerned popularly for the specialists in this eld. At present, the urgent problem (hotspot) is to improve penetration and quality of health care across the country.

Epidemiology
Epidemiology which is considered as the basic science of public health is the research of the distribution and determinants of events, health conditions, or diseases among populations and the application of the study to control health problems. When it comes to epidemiology, the majority of people naturally think of infectious diseases like cholera and AIDS. It concentrates on various health-related situations-diseases (e.g. u, epidemic hemorrhagic fever, depression), health risks (e.g. high blood pressure, obesity), injuries (e.g. tra c accidents) and some social problems (e.g. taking drugs, gambling).
Epidemiology policy plays a signi cant role in exploring the causes of conditions and preventing them. Prevention and elimination of infection, establishing and improving the public health system will be the priority of work in the study of epidemiology policy.

Children
Statistics result taken from WHO indicates that Risks to young children health mainly include low birth weight, malnutrition, not breastfeeding, overcrowded conditions, unsafe drinking water and indoor air pollution, overweight/obesity, poor diet physical inactivity including drowning, falls and burns are the main threats for the older children. Children are the vulnerable group in society, whose health and growth conditions caused wide public concern all over the world.
The health policy about children will tend to protect not only their physical health but also mental health.

Quality of life
Life quality obtains multidimensional experience and objective feeling. When people encounter some conditions in their life like job loss, illness etc., they will change the de nition of" quality of life". The pursuit of quality of life represents the desire of creating a happy life. Happiness can maintain people's mental health to some extent. The policy concentrating on "quality of life" will adopt some measures such as improving public infrastructure to emphasize the average happiness of population.

Keywords of bursts
Burst detection can detect large changes in the number of references at a given time. It is available to detect the decline or rise for a particular subject or keyword, which has been applied to our research. Figure 9 shows the top 15 keywords with the strongest bursts from 2011 to 2020. Initially, 2011 was regarded as the base period. The black line represents the learning period and the red represents the study outbreak period. It can be indicated that the internet, trends in this eld. Some keywords were tending towards stability after a while, which may be because some issues had been solved successfully or the social environments had changed a lot. Figure 9 shows the keywords timeline and cluster graph.

Discussion And Conclusions
From 2011, the number of yearly-publication has shown a downward trend and been stable eventually. The frequency of publication will maintain this trend in the coming period. There are 10 publication types used by 11 632 articles. English is the most signi cant and most widely used language in the research of health policy. America takes the lead in this eld with approximately 38% of publications. The researches about health policy follow the study model of "international cooperation" and has formed a relatively stable research group. The most productive institution is the University of London in the United Kingdom. The study shows that universities are the most important research institutions in this eld. At present, the most high-impact author is McKee Martin but there are no opinion leaders in the eld who can guide the development of the whole discipline. The 11 632 articles published in 1 786 journals are divided into 141 different subject categories. The research hot-spot are as following: health care, public health, epidemiology, children, and quality of life.
In conclusion, health policy is closely related to people's life. With constantly study, it has become a relatively mature research topic, but it doesn't mean the termination of the study. It remains to be properly explored and improved. Research in health policy will contribute to every aspect of people's lives as the international community pays more attention to health problems in the future.

Declarations
Ethics approval and consent to participate Not applicable Adherence to national and international regulations Not applicable

Consent for publication
Not applicable Availability of data and materials The datasets analyzed during the current study are available in the Web of Science repository Competing interests Figure 1 The Search Strategy Diagram Double graph overlay for journals covering two reference paths, the left were the journals of citing articles, the right were the journals of reference Key words co-appearance network Figure 9 the top 15 keywords with the strongest bursts between 2011 to 2020