Influential journals in health research: a bibliometric study

Background There is a wide range of intellectual work written about health research, which has been shaped by the evolution of diseases. This study aims to identify the leading journals over the last 25 years (1990–2014) according to a wide range of bibliometric indicators. Methods The study develops a bibliometric overview of all the journals that are currently indexed in Web of Science (WoS) database in any of the four categories connected to health research. The work classifies health research in nine subfields: Public Health, Environmental and Occupational Health, Health Management and Economics, Health Promotion and Health Behavior, Epidemiology, Health Policy and Services, Medicine, Health Informatics, Engineering and Technology, and Primary Care. Results The results indicate a wide dispersion between categories being the American Journal of Epidemiology, Environmental Health Perspectives, American Journal of Public Health, and Social Science & Medicine, the journals that have received the highest number of citations over the last 25 years. According to other indicators such as the h-index and the citations per paper, some other journals such as the Annual Review of Public Health and Medical Care, obtain better results which show the wide diversity and profiles of outlets available in the scientific community. The results are grouped and studied according to the nine subfields in order to identify the leading journals in each specific sub discipline of health. Conclusions The work identifies the leading journals in health research through a bibliometric approach. The analysis shows a deep overview of the results of health journals. It is worth noting that many journals have entered the WoS database during the last years, in many cases to fill some specific niche that has emerged in the literature, although the most popular ones have been in the database for a long time. Electronic supplementary material The online version of this article (doi:10.1186/s12992-016-0186-4) contains supplementary material, which is available to authorized users.


Background
The scope of public health history is dynamic and has been shaped by the evolution of diseases. In the last decades, health research has moved from the study of sanitary reforms and the control of infectious diseases, to the study of the impact of epidemic and contagious diseases, and to the inclusion of social action initiatives taken in response of epidemic disasters. Thus, the scope of health research has been expanded and broadened from a range of intellectual disciplines including the study of health economics [1], and social and political relations of health [2]. These intellectual contributions have been well documented in a range of professional journals.
For this reason, there is a wide range of intellectual work written about health research and it is time to evaluate its development and main characteristics. Bibliometric analysis can help determine trends and patterns of publications within a research discipline, identifying the focus of research and the national and international strengths and biases [4,5]. Over the course of the past few decades, several bibliometric analyses have been published regarding diverse topics in the literature of health research, including medicine and international health, where studies have tried to evaluate the contribution of different world regions in research production in infection diseases in terms of both quantity and quality [6], in respiratory research productivity where countries from Western Europe, Canada and Oceania had the best performance after adjustment for population and gross national income per capita [7], in cardiovascular research production where the results showed a promising trend of research productivity for developing world regions with the exception of Africa [8], and also look at the bibliometric profile of tropical medicine and international health [9]. In health informatics studies have included an up-to-date view of the telemedicine and telehealth literature analyzing the changes in content themes [10], assessing the impact of grants in the contribution to scientific knowledge of health information technologies on patient safety and quality of care outcomes [11], quantifying the number of publications on electronic health records and their changes over time [12], and studying the contribution of individual countries to leading journals in medical informatics [13]. Among occupational health, articles have helped to identify the most pertinent journals in the practice of occupational health and to develop search strategies that facilitate finding occupational health intervention studies [14][15][16]. There are also bibliometric analysis published in health management that investigate the attention and progress of strategic management in the literature [17], in health economics, studies have reported the growth of health economics literature and the change in topics and geographical focus of health economics [18][19][20]. Bibliometric studies in health service research have looked for trends, gaps and characteristics when comparing among different regions [21,22], in the same line other studies have assessed the scientific production in health policy [23,24], in primary health [25,26], in epidemiology [27,28], in environmental health [29][30][31], in public health and preventive medicine [32,33], in preventive medicine, occupational and environmental medicine, epidemiology, and public health [34], and also public in health research in specific countries or regions [35][36][37][38][39][40][41][42]. This literature has become relevant today perhaps due to the diverse disciplines that are engaged in health research and its importance in order to monitor and disseminate the scientific achievements from the research work.
In this current study we aim to expand the scope of analysis of health research even more, identifying and quantifying the scholarly publications in the field and subfield approaches of public health, environmental and occupational health, health management and economics, health promotion and health behavior, epidemiology, health policy and services, medicine, health informatics, engineering and technology and primary care. Our main goal is to produce an overview of the leading journals in health research literature in the world for a time frame of 25 years from 1990 to 2014. There are many aspects that can indicate the value of a journal; in this study we use the number of citations and their impact factor to reflect the quality of the review process and its popularity in the scientific community. Findings from this research may assist researchers to identify top performance journals in a subject area, learn more about the subfields of health research, and identify emerging areas of research to locate areas of potential study.

Methods
There are different approaches for classifying the bibliographic material. Bibliometrics is one of the most common approaches [43,44]. In order to represent the results, the analysis uses a wide range of indicators that measure the quality of the publications. Currently, there is no general agreement on the optimal method for measuring research because depending on the perspective considered an indicator may be better than another one. Therefore, the current literature deals with many indicators that have appeared during the last years [45][46][47].
In this study, the aim is to provide a general picture in order to get a complete overview that can adapt to the interests and perspectives of each specific reader. Thus, several indicators are considered including the total number of publications and citations, the citations per paper, the hindex [48] and the number of papers that a journal has among the most cited ones in a specific field. Note that the most cited papers are found in Web of Science (WoS) by ordering the results of a search from the most cited papers to the less cited [49].
The study uses the WoS database in order to search for the information. WoS is usually regarded as the most influential database for scientific research because it includes those journals that are generally recognized with the highest quality. It was originally created by Eugene Garfield with the name of Institute for Scientific Information (ISI the first one appears both in the Science Citation Index and in the Social Science Citation Index. These four categories encompass 363 journals. Since these four categories are very broad, the study divides health research in nine categories in order to get a deeper picture of the leading journals in each subfield. However, it is worth noting that sometimes it was not clear where to classify a journal because its scope may include two or three subfields. In any case, the analysis considers a Global Ranking (GR) where all the journals are ranked together. This allows comparison between subfields when needed. The nine categories are: Although the work considers many indicators, the ranking is carried out according to the total number of  citations. The main reason for this is that the citations measure the influence that a journal has in absolute terms. Other alternatives could be considered including the citations per paper and the h-index. The main limitation of this indicator is that it does not take into account the number of papers that have generated the number of cites. However, the rest of indicators included in the tables allow the reader to get a comprehensive overview of each journal although the ranking is focused on the number of citations. The analysis focuses on the last 25 years (1990-2014). The main reason is because this time period is representative of the latest developments of the field. In order to take into account the influence from a classical perspective, the study includes an indicator that shows the number of articles that a journal has among the 200 most cited articles published before 200. This allows the reader to see those journals that were very influential before and see if they are still leading the field or not. Note that the search process carried out in WoS has been developed between March and August 2015. The types of documents considered are: articles, reviews, notes and letters.

Results
This section presents the main bibliometric results found in WoS for 363 health research journals from 1990 to 2014. The results are ordered by category and each table contains the 20 or 10 most cited journals of each category (see the Additional file 1 for the full list of journals).

Public health
Public health refers to the activities to prevent diseases, promote health, and prolong life for the whole population [50]. Therefore, the main objective of public health is assuring conditions for the people in order to be healthy. It is at the core of health research and consequently there are many journals devoted to increase knowledge and raise awareness on this topic. Table 1 shows the most influential journals among this category.  The journal that has received more citations and the higher h-index in this field is the American Journal of Public Health with 302,196 citations and an h-index of 198; followed by Social Science & Medicine with 281,663 citations and an h-index of 163. These two journals dominate the number of citations in the field with more than 50 % of all the cites. Despite these elevated numbers, the highest average citation rate per paper, impact factor, and 5-year impact factor is for the Annual Review of Public Health.
Analyzing the T50 and T200 ranking results, Social Science & Medicine is in the top positions with 17 papers or 34 % of the papers in the T50 ranking of the category, followed by the American Journal of Public Health with 30 % of the papers in the T50. The same journals have 9 and 14 papers respectively in the T200 ranking. Note that all the journals of the category have an h-index bigger than 20, reflecting its influence and productivity.

Environmental and occupational health
Environmental health studies the impact of our surroundings in health, while occupational health studies all aspects of health and safety in the workplace. This category includes journals regarding the understanding of the impact and control of environmental and occupational hazards on human health and society. Table 2 presents the results for this category.
The journal Environmental Health Perspectives has the highest results in all the measures, with 311,509 citations that are far from any other journal in the category, an h-index of 192, and an impact factor of 7.029. It has also 80 % of the papers in the T50 ranking, and 22 papers in the T200 ranking of the most cited papers in all fields of health.

Health management and economics
This category includes journals related to the economics and management of health and healthcare (see Table 3).
Medical Care is the journal positioned number one in this category according to the number of citations, hindex, average citations per paper, and 5-year impact factor. It has 62 % of the papers among the 50 most cited in the category, and 16 out of the 200 most cited in all fields of health. However, the highest impact factor in the category is for Pharmaeconomics, positioned fourth according to the total number of citations.

Health promotion and health behavior
Health promotion and health behavior refers to the role of behavioral and social influences to address current and emerging public health problems. Table 4 shows the most influential journals in this category.
As we can see in Table 4, there are two journals leading the citation ranking: the American Journal of Preventive Medicine and Preventive Medicine with 115,942 and 111,066 citations respectively. Also these two journals have an h-index over 100. The Tobacco Control Journal has the highest impact factor of 5150; however, the American Journal of Preventive Medicine has the highest 5-year impact factor. Additionally, the American Journal of Preventive Medicine has 13 studies in the T50 ranking and five in the T200.

Epidemiology
Epidemiology is a basic science of public health. It studies the distributions and determinants of health problems in different groups of people. Epidemiological information is used to plan and evaluate strategies to control or prevent diseases. Table 5 presents the main journals in this category.
The American Journal of Epidemiology is in the first place of this category, and also among all the categories according to the global ranking (GR). It has also the highest h-index of all categories, reflecting his influence and impact. It is followed by the Cancer Epidemiology Biomarkers & Prevention and the Journal of Clinical Epidemiology that occupy positions 5 and 7 in the GR. The highest impact factor and 5-year impact factor is for the Epidemiology journal with values of 6178 and 6894 respectively. Regarding the T50 ranking, the Journal of Clinical Epidemiology has 46 % of the most cited papers in this category and the American Journal of Epidemiology has 22 %. In the T200 ranking, this category has 39 out of the 200 most cited journals in all the fields, eight are from the American Journal of Epidemiology and 16 of the Journal of Clinical Epidemiology.

Health policy and services
This category includes journals from multidisciplinary fields of scientific investigation that study among others the rising demand for health services, how to improve their quality and efficiency, and rigorous policy analysis that ultimately impact our health and well-being (see Table 6). Even though Health Affairs is the most cited journal, the Milbank Quarterly has the highest TC/TP ratio, impact factor, and 5-year impact factor, being the most influential in the category. It is also worthiest to notice that Quality of Life Research has 15 out of the 50 most influential papers in the category, followed by Health Affairs with 11 and Milbank Quarterly with eight. Quality of Life Research and Milbank Quarterly have three papers each in the T200 ranking.

Medicine
Medicine is one of the world's oldest categories in the arena of health research, allowing scientists and physicians to communicate their advances. The results of this category are displayed in Table 7.
American Journal of Tropical Medicine and Hygiene is the most influential according to its total number of citations of 178,865. However, the h-index is the same for the American Journal of Tropical Medicine and Hygiene and the Journal of General Internal Medicine, but the TC/TP ratio and impact factor is higher for the latter. The highest impact factor and 5-year impact factor is for the Implementation Science journal. In the T50 ranking, Academic Medicine appears with 12 papers, the American Journal of Tropical Medicine and Hygiene with 9, and the Journal of General Internal Medicine has 14 in this ranking and three in the T200 ranking.

Health informatics, engineering and technology
This category involves the research and integration of resources, devices, and methodologies to optimize the use of information to provide a better healthcare. The Top ten journals in this category are shown in Table 8.
The Journal of the American Medical Informatics Association is the most influential in this category with the highest number of citations, h-index, TC/TP ranking, impact factor, 5-year impact factor. Additionally, it has 52 % of the papers among the 50 most cited of the category, but none in the T200. Health Physics and Health Technology Assessment have one paper each in the T200 ranking.

Primary care
Primary care is all the regular health services and social services that are available for the population, and its research is at the cornerstone for building a strong healthcare system. Table 9 presents the Top ten journals in this category.  The most cited journal is the British Journal of General Practice, followed by the American Family Physician, the Journal of Family Practice, and Family Practice. The highest h-index is for the Journal of Family Practice. While these four papers are the most cited, Annals of Family Medicine is the journal with the highest impact factor, and 5-year impact factor. Among the 50 most cited papers in this category, the Journal of Family Practice has 34 % of them, followed by Annals of Family Medicine with 18 %, the British Journal of General Practice with 16 %, and Family Practice with 12 %. There are two journals in the T200 ranking with one paper each, which are the Journal of Family Practice and Family Medicine.

Comparison between fields
Finally, let us provide a general picture of the publication and citation structure of each health category. Table 10 presents the results.
Epidemiology is the most influential category over the last 25 years with the highest number of citations, citations per paper, h-index and the largest number of articles among the 200 most cited before and after 1990. Public Health also obtains very remarkable results being the category with the largest number of articles. However, the category with the highest number of journals is Health Promotion and Health Behavior.

Discussion and conclusions
This study showed some remarkable viewpoints about health journals currently indexed in WoS database between 1990 and 2014. This analysis shows the results obtained by health journals under a wide range of bibliometric indicators. This is very useful to see the general results from a broader perspective than the Journal Citation Reports of WoS. Particularly, this is very useful for PhD students and newcomers in the field in order to get a general orientation of the leading journals in health research.
The results provide a general picture of the current position of the leading journals in this field for the nine categories analyzed, which can be rank in terms of total papers as follows: (1)      Behavior. This indicates that the journals considered in the study have different profiles with a wide variety of objectives. Almost all the leading journals are published in English although some journals may also publish in some other popular European languages including German, Spanish, French and Italian. Note that many journals have entered the WoS database during the last years although the most popular ones have been in the database for a long time.
In conclusion, by bibliometric methodology, the findings and suggestions of this study can help scientific researchers understand the performance and trends of health research globally. With the help of these findings researchers can make informed decisions of their research directions, in terms of identifying top journals of the discipline, and choose exchange platforms for their research. This study also helps to learn more about the subfields of health research, and identify emerging areas of research today such as public health, health promotion and health behavior and epidemiology, and also how most areas of health research have started to decline in number of citations from 2006.
From a general perspective, health research is a very broad area that includes a wide range of topics. This article classifies the material according to some of the most significant topics. However, it is worth noting that more specific topics could also be considered because each journal considers specific topics that do not depend on the topics followed by other journals. Moreover, the Table 9 Most influential journals in Primary Care R Journal name  TC  TP  H TC/TP Year Volume IF  IF5  T50 T200 T200* GR First year study assigns each journal to one category but sometimes the journal could also be considered in another category. For solving this issue, the last column of each table (GR) considers the global ranking that each journal obtains when merging all the journals in the same list and ordering according to the number of citations. This allows comparison between journals from different categories. But note that each category or group of journals may have a different profile with a different volume of publications and citations. Therefore, it is not easy to compare journals with different topics and categories. Finally, recall that WoS has several limitations when classifying bibliographic material that should also be considered in this article [49]. Additionally, many other issues may affect research in this field including open access and electronic journals. Note that only those included in WoS are considered in the analysis.

Additional file
Additional file 1: Table S1. Public Health.