Impact of Article Language in Multi-Language Medical Journals - a Bibliometric Analysis of Self-Citations and Impact Factor

Background In times of globalization there is an increasing use of English in the medical literature. The aim of this study was to analyze the influence of English-language articles in multi-language medical journals on their international recognition – as measured by a lower rate of self-citations and higher impact factor (IF). Methods and Findings We analyzed publications in multi-language journals in 2008 and 2009 using the Web of Science (WoS) of Thomson Reuters (former Institute of Scientific Information) and PubMed as sources of information. The proportion of English-language articles during the period was compared with both the share of self-citations in the year 2010 and the IF with and without self-citations. Multivariable linear regression analysis was performed to analyze these factors as well as the influence of the journals‘ countries of origin and of the other language(s) used in publications besides English. We identified 168 multi-language journals that were listed in WoS as well as in PubMed and met our criteria. We found a significant positive correlation of the share of English articles in 2008 and 2009 with the IF calculated without self-citations (Pearson r=0.56, p = <0.0001), a correlation with the overall IF (Pearson r = 0.47, p = <0.0001) and with the cites to years of IF calculation (Pearson r = 0.34, p = <0.0001), and a weak negative correlation with the share of self-citations (Pearson r = -0.2, p = 0.009). The IF without self-citations also correlated with the journal‘s country of origin – North American journals had a higher IF compared to Middle and South American or European journals. Conclusion Our findings suggest that a larger share of English articles in multi-language medical journals is associated with greater international recognition. Fewer self-citations were found in multi-language journals with a greater share of original articles in English.


Introduction
The impact factor (IF) is a measure of an academic journal's international standing and is influenced by several well-known parameters. Although sometimes harshly criticized, the IF is widely recognized as a quantitative measure of a journal's reputation and the importance of published items [1]. Therefore, journals attempt to increase their IF in various ways. Some critics believe that journals try to inflate their IF by encouraging self-citations and preferring articles from authors who cite more articles from the journal to which they submit [2].
A study investigating this concern has shown that, at least for anesthesiology journals, there is no broader trend to do so [3].
It is a well-known fact that there is a correlation between a journal's IF and its language and that it is stronger than the association of IF and country of origin [4,5]. Mueller et al. [4] report that articles written in English are cited more frequently and think it to be imperative that scholars be aware of this language bias, which has also been described by Gregoire et al. [6].
We suggest that a low proportion of self-citations to all citations in a journal is a good indicator of the journal's international visibility, especially when compared with the journal's IF. Therefore, our hypothesis was that multi-language journals with a greater share of English articles have a higher IF without self-citations, on the one hand, and a smaller share of self-citations, on the other hand, as a marker of international recognition.

Methods
We analyzed all medical journals that published research manuscripts in English and at least one other language in the years 2008 and 2009. For the analysis we used data from PubMed as well as from WoS. PubMed provided information on the amount of English and non-English language articles as well as on the other language(s) used (query: ). WoS provided the total number of cites and self-cites, the number of cites and self-cites to years used in the impact factor (IF) calculation, the overall IF and the IF without self-cites, and the country of origin.
The first step was to identify the non-English and multilanguage journals listed in both PubMed and the WoS Journal Citation Reports. First, we searched PubMed (http:// www.ncbi.nlm.nih.gov/pubmed/) for all journals publishing non-English articles in the years specified above (query: In addition, we wanted to ascertain whether or not the journal's country of origin had any significance. Therefore we divided the territories into five groups: 1) Northern and Western Europe, 2) Eastern and Southern Europe, 3) North America, 4) Middle and South America, and 5) Asia and Africa.
All data were collected in an Excel table. The statistical analysis was done by an experienced statistician implementing linear regression analysis and Pearson tests for the comparison of the percentage of English articles to impact factor, percentage of self-citations and impact factor without self-citations, respectively. Multifactorial regression analysis and ANOVA test was used to determine the influence of the percentage of English articles, the percentage of self-citations and the number of cites to years used in impact factor calculation on the impact factor without self-citations. We applied a multivariable linear regression analysis to determine the influence of the territory and language used on the results. In order to account for differences between geographic areas those were included as a categorical covariate into the model with Northern and Western Europe as reference category. The used statistic programs were GraphPad Prism v 6.0 and SPSS 20. Statistical significance was assumed for p < 0.05.

Results
A total of 127,852 non-English articles were published by 709 journals in 2008 and 2009. Only 216 of these journals were registered in the WoS database (see Figure 1). After exclusion of all single-language and nonmedical journals registered in WoS and PubMed, 168 journals were left for analysis. Table 1 lists the general characteristics of the 168 journals we investigated.
We found a significant, though moderate, positive correlation of the share of English-language articles in the years of interest with the IF calculated without self-citations (Pearson r=0.56, p = <0.0001), a weaker correlation with the overall IF (Pearson r = 0.47, p = <0.0001), and the cites to years of IF calculation (Pearson r = 0.34, p = <0.0001) and a weak negative correlation with the share of self-citations (Pearson r = -0.2, p = 0.009) (see Figures 2-5). We also found a significant correlation of the share of self-citations and the share of English articles on the IF without self-citations: the less selfcitations and the more English articles the higher the IF without self-citations (see Table 2). The IF without self-citations was also associated with the journal's country of origin as shown in Table 3: North American journals had a higher IF when calculated without self-citations.

Discussion
Our analysis of 168 medical multi-language journals has revealed a significant association of the share of original English-language publications in a journal with the proportion of self-citations and its IF: the more English-language articles, the smaller the share of self-citations and the higher the IF. This finding suggests that a greater share of articles in English improves international recognition and therefore fewer selfcitations are needed to artifactually increase the IF. On the other hand, this may be caused by authors citing articles in their mother tongue when writing articles in the same language. However, when preparing an English article an author would rather not cite articles written in another language. We also observed an influence of journals' countries of origin and the  languages used besides English on the results: journals originating in North America tend to have a higher IF, followed by journals from Northern and Western Europe. However, European journals may catch up with America in the future [7]. Most likely, our findings can be ascribed to the number of potential readers that depend on the article language, the country of origin, and the historically developed structures and reputation of medical societies and journals. Therefore, it might be useful for the editors of a journal from a small country to know that articles in English can enhance their journal's international visibility and IF. However, journals may aim a better IF by increasing the share of self-citations but that has no influence on the number of potential readers and the possible international recognition of a journal. This is especially important for small national journals that might lose IF in comparison to top-ranked journals [8].
The advantages and disadvantages of using the IF as a measure of a journal's recognition and quality are controversially discussed in the medical literature [9][10][11][12][13][14]. Basically, the IF is the frequency of citations to the average number of articles published in a scientific journal in a specific period of time, for example the year 2010. The actual impact factor, therefore, is calculated by dividing the total number of an indexed journal's current year citations to articles in the journal published in the previous two years by the number of "citable items" (e.g., original research articles, reviews or notes) published by the journal in the same period of time. Recent years have witnessed some studies investigating citation practices and trends in all or specific parts of the medical literature as well as potential influences on the IF. The online status of an article, for example, has been shown to affect the IF [15,16]. Even the length of an article's title is supposed to have an influence on the number of received citations: the longer the title, the more citations [17]. A possible influence of industry on the IF has been discussed in a recent publication [18].
There might be some other influences on the results that are hard to measure. The quality of a publication may differ between non-English and English articles because high quality studies are potentially more likely to be published by the authors in English because of the increased international recognition. On the other hand, in case of lower quality studies, the same authors might be more likely to choose his native language for publication. The medical category of the journal's Self Citations and Impact Factor PLOS ONE | www.plosone.org WoS provides (e.g., internal medicine or radiology) is also an interesting parameter affecting IF and citation characteristics. However, 37 of the 168 journals analyzed here are listed in two or more categories. Thus, a clear allocation of all journals and therefore a robust statistical analysis of the influence of category is not possible. Some authors doubt that there is a correlation between the share of English-language articles and IF [19,20]; however, it must be noted that these authors analyzed only a selected journal or journal category. Our findings include the available data of all multi-language medical journals with articles published in 2008 and 2009. However, our analysis covers only a short period in time. Further investigations need to be conducted to compare the development of the share of English-language articles in multilanguage journals over an extended period with changes in IF and self-citation practices [21]. Such studies might provide a different perspective on the issue of English and native language use in the medical literature. Furthermore, it might be interesting to proceed to a publication-based analysis although the assessment of all 127,852 publications would be an enormous challenge. Unfortunately, only about 30% (216 of 709) of the journals PubMed lists were registered in WoS. For example, there were many Chinese and Russian journals with no available citation data in WoS. Nevertheless, we believe that our sample is adequate for getting a robust overview, at least concerning multi-language journals published in Europe and those published elsewhere in Spanish or Portuguese. The increasing use of English in the medical literature has been criticized repeatedly and harshly [22]. Therefore, it is left to authors and publisher to carefully consider the pros and cons and decide whether or not an English article is suitable for a particular carrier or journal.

Conclusion
Publishing academic papers in English in multi-language medical journals increases the international visibility and recognition as measured by the IF. At the same time, more English-language articles lead to a smaller share of selfcitations required by multi-language journals.   Table 2. Correlation of the share of English-language articles, share of self-cites and the number of cites to years used in IF calculation to the IF without self-citations; the share of English-language articles had a moderate positive influence, whereas the share of self-citations exerts a negative one: The more English articles and the less self-citations the higher the IF without self-citations.