Is the science citation index US-biased?

The Western European science policy establishment often claims that US articles are more frequently cited than articles of the European Union's scientists because they are published in journals with a large number of US publications and that these journals are forming the ‘core’ of the SCI.For the disciplines covered by the SCI, no significant correlation has been found between the ratio of the average number of citations per publication for publications with at least one EU address and at least one US address, respectively, on the one hand, and, on the other hand, the ratio of the corresponding number of publications per journal.