Citation advantage of Open Access articles likely explained by quality differential and media effects

In a study of articles published in the Proceedings of the National Academy of Sciences, Gunther Eysenbach discovered a significant citation advantage for those articles made freely-available upon publication (Eysenbach 2006). While the author attempted to control for confounding factors that may have explained the citation differential, the study was unable to control for characteristics of the article that may have led some authors to pay the additional page charges ($1,000) for immediate OA status. For instance, of the 1,492 original articles (212 OA) tracked in Eysenbach’s study, OA articles were more than twice as likely to be featured on the front cover of the journal (3.3% vs. 1.4%).