Citation Advantage For OA Self-Archiving Is Independent of Journal Impact Factor, Article Age, and Number of Co-Authors

Eysenbach has suggested that the OA (Green) self-archiving advantage might just be an artifact of potential uncontrolled confounding factors such as article age (older articles may be both more cited and more likely to be self-archived), number of authors (articles with more authors might be more cited and more self-archived), subject matter (the subjects that are cited more, self-archive more), country (same thing), number of authors, citation counts of authors, etc. Chawki Hajjem (doctoral candidate, UQaM) had already shown that the OA advantage was present in all cases when articles were analysed separately by age, subject matter or country. He has now done a multiple regression analysis jointly testing (1) article age, (2) journal impact factor, (3) number of authors, and (4) OA self-archiving as separate factors for 442,750 articles in 576 (biomedical) journals across 11 years, and has shown that each of the four factors contributes an independent, statistically significant increment to the citation counts. The OA-self-archiving advantage remains a robust, independent factor. Having successfully responded to his challenge, we now challenge Eysenbach to demonstrate -- by testing a sufficiently broad and representative sample of journals at all levels of the journal quality, visibility and prestige hierarchy -- that his finding of a citation advantage for Gold OA (articles published OA on the high-profile website of the only journal he tested (PNAS) over Green OA articles in the same journal (self-archived on the author's website) was not just an artifact of having tested only one very high-profile journal.