Publication of research findings in a particular language.
The English language has been the predominant language in medical research. Publication in other languages can sometimes be regarded as of secondary importance. Studies publishing positive results might also be more likely to publish in English. Reading and using only English language research could provide a biased assessment of a topic, and can lead to biased results in systematic reviews.
A 1997 Lancet study looked at the language used to publish the results of randomized controlled trials performed in German-speaking regions of Europe. The authors found that trials with statistically significant results were more likely to be published in English than in German.
Research looking at the effect of language bias on the findings of systematic reviews has not identified quantifiable evidence of language bias on the results but has found a statistically significant difference in the proportion of positive and negative result papers published in English versus other languages. One third (35%) of German language articles reported significant results compared with two-thirds (62%) of English-language articles (p = 0.002).
Researchers should attempt to discover and use research published in languages other than their own or other than in English. Ideally, literature reviews should not exclude research articles on the basis of the language they are published in.
Catalogue of Bias Collaboration, Brassey J, Spencer EA, Heneghan C. Langauge bias. In: Catalogue Of Bias 2017: https://www.catalogueofbias.org/biases/language-bias