Xiaolin Tong M.D., Fengmei Lian M.D., Department of Endocrinology, Guang’anmen Hospital, China Academy of Chinese Medical Sciences, No.5 Beixiange Street, Xicheng District, Beijing 100053, China, e-mail: xiaolintong_66@126.com (X. Tong); lfm0226@sohu.com (E Lian)

This work was supported by the National „Twelfth Tive-Year” Plan for Science & Technology (2013BAI02B10).

Introduction

In recent years, tire field of endocrinology and metabolism have grown significantly [1, 2]. This has been a worldwide effort; however, some countries have contributed more than others. It should not be expected that each country produce tire same amount of publications because different countries have very different capabilities in terms of financial research resources, scientific research programs, and established healthcare systems [3, 4].

Scientific progress can be assessed according to the number of publications that are produced by scientific research groups. Progress in the field of endocrinology and metabolism worldwide can be analysed by assessing the numbers of publications produced by authors in different countries. Also, bibliometric analysis can be used to investigate trends in scholarly publications and the relative importance of articles on a specific topic. Bibliometric analysis has been used to determine national contributions to research fields including oncology [4], cardiovascular disease [5], rheumatology [6], nutrition and dietetics [7], diabetic retinopathy [8], emergency medicine [9], critical care medicine [10], anaesthesia [11], plastic and reconstructive surgery [12], foot and ankle research [13], and arthroscopy [14].

Research productivity in the field of endocrinology and metabolism, however, has not been assessed to date. The aim of this study was to analyse research productivity worldwide to uncover national differences in contributions to the study of endocrinology and metabolism from 2010 to 2014.

Material and methods

In Journal Citation Reports (JCR) for the year 2013 established by the Institute for Scientific Information [15] a total of 124 journals in the subject categories of „endocrinology & metabolism” were included in this study (Supplement 1).

The Web of Science database was searched on 8 April 2015 to identify publications in the field of endocrinology and metabolism. The Web of Science is the world’s leading database for scientific publications, and citations and other academic impact information is included in this database, which makes it a widely used source for studies on scientific productivity [7-10, 12]. Articles published in 124 journals from January 2010 to December 2014 were identified. The search was conducted for original articles and reviews, and articles that were letters, editorials, or corrections were excluded. The titles of the journals were used to perform a literature search in Web of Science. For each article, tire source nation was considered as the nation of the institutional affiliation, unless there was more than one institution, in which case the institution of the corresponding authors was considered as the source nation.

Quantification of research productivity was based on the number of published articles. The total number of citations of some articles was a quality indicator. The primary outcome of the study was the number of original articles originating from each country. Countries were then ranked according to their productivity as expressed by the number of publications. Countries were labelled as high income, upper middle income, lower middle income, and low income according to the categories set by the World Bank [16]. Gross national income per capita determined the income levels, and $12,746 or more was considered high income, $4,125 to $12,745 was considered upper middle income, $1,046 to $4,125 was considered lower middle income, and $1,045 or less was considered low income. The percentages of articles for each category were then calculated.

Countries producing at least 1% of the total publications were considered as the main productive countries, and further analysis of these countries was performed including the total number of publications, publications per capita, total citations (the number of articles multiplied by the number of citations), and the mean citation number. Statistics on population sizes and gross domestic product (GDP) from the Central Intelligence Agency of the United States and the Word Bank for the most recent report were used in the study [17]. The top five countries in terms of publications and the top five journals were listed.

Since we were not employing hypothesis testing but were only describing trends, only descriptive statistics were used, e.g. sum, average, and percentage. A Spearman’s test was used for correlation analysis [10, 13, 14], SPSS version 19.0 (SPSS Inc., Chicago, IT, USA) was used for all statistical analyses and p < 0.05 was considered as significant.

Results

In the years 2010-2014 the total number articles on endocrinology and metabolism identified in the database of Web of Science was 79,394. In 2010 14,905 articles were published, and in 2014 16,201 articles were published. This was a 1.09-fold increase in the publication rate.

Based on the number of publications, 124 countries contributed to the science of endocrinology and metabolism. Authors in the United States published the most articles (21,740/79,394, or 27.38%), authors in China published the second most (5,736/79,394, or 7.22%), and this was followed by Italy (4,529/79,394, or 5.70%), the United Kingdom (4,446/79,394, or 5.60%), and Japan (4,397/79,394, or 5.54%). Figure 1 shows the productive regions on a world map, and North America, East Asia, and Europe are clearly most prominent. A total of 65,323 (82.28%) articles were published in high-income countries, 14,006 (17.64%) articles were published in high middle- and low middle-income countries combined, and only 65 (0.08%) articles were published in low-income countries (Fig. 2). There was a significant correlation (p < 0.01) between the number of publications and population size and GDP (r = 0.442 and r = 0.834, respectively, Fig. 3).

Figure 2. Publications grouped by gross national income 2010 to 2014
Rycina 2. Publikacje pogrupowane według produktu krajowego brutto w latach 2010-2014

Figure 3. Scatter plot showing the association of publication activity in the field of endocrinology and metabolism with population and GDP from different countries
Rycina 3. Wykres punktowy ilustrujący związek aktywności publikacji w dziedzinie endokrynologii i metabolizmu z populacją í PKB dla różnych krajów

Twenty-one countries were seen as main productive countries (producing at least 1% of the total number of articles). These 21 countries published 70,782 of the 79,394 (89.15%) articles (Table I). Of all the main productive countries, the United States had the highest number of citations (260,934); the United Kingdom had 52,068 citations, and Italy had 37,340 citations. Regarding the mean number of citations, the ranking was as follows: the United States (12), the United Kingdom (11.71), and Switzerland (11.67). Most of the articles had authors from high-income countries (17). Upper middle-income countries were the second, twelfth, and sixteenth (China, Brazil, and Turkey, respectively) ranked nations. India, which is a lower middle-income country, was the 18th ranked nation.

Denmark produced the highest number of publications per million population (249.95), Sweden had 152.51 publications per million population, and the Netherlands had 126.97. When GDP was considered, Denmark ranked the highest with 42.10 publications, Greece had 34.13, and the Netherlands had 26.78. After adjustment for GDP, the United States, China, and Japan ranked relatively low, even though they have large economies.

Table II shows the publications from the five top ranked countries. The most popular journal for the United States was the Journal of Clinical Endocrinology & Metabolism·, the most popular journal for China was Biological trace Element Research, and the Journal of Endocrinological Investigation was popular in Italy. The journal Diabetic Medicine was the most popular in the United Kingdom, and Endocrine Journal was popular in Japan. The Journal of Clinical Endocrinology & Metabolism was popular in three of the top five countries.

The top five journals and the five most productive countries are listed in Table III. Regarding publication in the top five journals, the United States was most productive. Also, the United States was one of the top five countries represented in the top five journals. The United Kingdom was one of the top five countries represented in four of the five top journals, and Italy was represented in three of the five top journals.

Discussion

Developments in science and technology have produced great advances in the field of endocrinology and metabolism, and the scientific contributions to this advancement have been from researchers throughout the world. Scientific publications report new knowledge in the field and also indicate the productivity of the researchers. Bibliometric methods can be used to evaluate research productivity, and contributions from various areas in the world can be assessed [4-14]. Our study was the first to use bibliometric evaluation to analyse the contributions of various countries to research in endocrinology and metabolism.

We found that authors in the United States published the greatest number of articles on endocrinology and metabolism compared to other countries. This result indicates that the United States plays an important role in scientific endeavours on endocrinology and metabolism. The United States has been a leader in biomedical research for decades, including endocrinology metabolism as well as other subfields in biomedical research [9-14].

In addition to producing the most articles overall, articles from the United States have the most citations (260,934) of endocrinology and metabolism publications, as well as one of the highest mean number of citations (12). This suggests that the United States is very productive but also produces high quality publications. The per capita number of articles produced in the United States is also very high (68.17 per million persons). The results of our study demonstrated that the United States is the most productive country in the world in the field of endocrinology and metabolism.

A „10/90” divide has been used to describe the ratio of contributions from non-high- versus high-income countries [18]. This ratio has been identified in many medical fields [9-12]. In our study, we found a slightly higher proportion for middle-income countries. This difference may be attributed to four middle-income countries, i.e. China, Brazil, Turkey, and India [5, 9, 11]. An increasing importance in biomedical research has been recognised for these countries [9, 11, 19, 20]. The significant development that has occurred in these middle-income countries should be recognised [9, 11]. With further economic development, these countries could improve their rank in the future by improving their endocrinology and metabolism research. Government policy, poor medical infrastructure, lack of research funds, and few researchers may be the root causes of poor research productivity in endocrinology and metabolism in low-income countries, which only produced 65 articles during the period of this study.

Some European countries, such as Denmark, Sweden, the Netherlands, and Greece, were seen to be very productive when the results were normalised to population size and GDE The productive countries are nearly all developed. Although China is the second productive country in the number of total articles, the number per million population is rather small, which is followed by India. This indicates that the relative productivity remains very low in these countries and further growth is needed. It may be more informative to normalise by the number of researchers in each country rather than population size, but it is very difficult to obtain information on the number of researchers in the field of endocrinology and metabolism in each country.

For the five top ranked countries, the most popular journal in the United States was the Journal of Clinical Endocrinology & Metabolism, for Italy it was the Journal of Endocrinological Investigation, for the United Kingdom it was Diabetic Medicine, and for Japan it was Endocrine Journal. Each of these journals is published in the associated country, which means that there are probably more submissions from researchers in that country. Both the United States and the United Kingdom were represented at least four times as of the top five countries in the top five journals. This indicated the influence of these countries in the field of endocrinology and metabolism.

This study had some limitations. The first limitation is the inclusion of medical journals based on JCR criteria. Non-JCR-cited journals were not included in the article search, even though non-JCR-cited journal articles contributed to scientific production. Second, basic science and general internal medicine journals in categories of the JCR other than „endocrinology & metabolism” may have published endocrinology and metabolism-related articles, but they were not included in this study. However, our bibliometric analysis included 124 endocrinology and metabolism journals, and these journals represent the major journals reporting research in the field of endocrinology and metabolism.

Conclusions

In summary, we evaluated the national research productivity in the field of endocrinology and metabolism during a five-year recent period in this study. The results of the present study showed that the majority of publications were published by high-income countries, while relatively few publications were from low-income countries. When considering the number of publications produced overall, the United States is the most productive country in the world regarding endocrinology and metabolism. However, when the results were normalised to population size and GDP, some European countries might be considered to be more productive.

Acknowledgement

We would like to thank Zhiwei Jia and Yaohong Wu from the Navy General Hospital, Beijing, China for modifying the manuscript.

Supplement 1. List of considered journals under the topic heading „endocrinology & metabolism” on Web of Science
Suplement 1. Lista rozpatrywanych czasopism pod względem nagłówka tematycznego „endokrynologia i metabolizm” w Web of Science