Impact factor trends for general medical journals: non-English-language journals are lagging behind

BACKGROUND: The impact factor (IF) is a common citation metric used for evaluating and comparing scientific journals within a certain field. Previous studies have shown that IFs are increasing. However, rates may depend on journal publication language. The aim of this study was to determine IF values and trends for general medical journals, comparing non-English-language with English-language journals. METHODS: For all journals categorised as "medicine, general and internal" (n = 150) in the Journal Citation Reports (JCR), publication language, country of origin and IFs for the last 10 years were recorded (2001-2010). Data were classified, analysed descriptively and compared using non-parametric tests. RESULTS: From 2001 to 2010, IFs increased for English-language and non-English-language journals (p <0.001). During the 10-year study period, IFs were higher for English-language than for non-English-language journals (p <0.001). The proportion of non-English-language journals included in the JCR was 12.2% in 2001 and 18.0% in 2010 (p =0.28). INTERPRETATION: From 2001 to 2010, IFs increased significantly for English-language and non-English-language journals. When comparing IF values year-by-year (2001-2010), IFs were significantly higher for English-language than for non-English-language journals. In an international scientific community with English as the universal language of science, non-English-language journals should consider changing publication language, and adopt either a bi- or a monolingual approach. Publishing in English will increase citation counts and thus IFs, but, more importantly, scientific findings will be accessible to a much wider audience.