Language biases in the coverage of the Science Citation Index and its consequences for international comparisons of national research performance

Empirical evidence presented in this paper shows that the utmost care must be taken in interpreting bibliometric data in a comparative evaluation of national research systems. From the results of recent studies, the authors conclude that the value of impact indicators of research activities at the level of an institution or a country strongly depend upon whether one includes or excludes research publications in SCI covered journals written in other languages than in English. Additional material was gathered to show the distribution of SCI papers among publication languages. Finally, the authors make suggestions for further research on how to deal with this type of problems in future national research performance studies.