I applaud and welcome the results of the Eysenbach (2006) study on 1492 articles published during one 6-month period in one journal (PNAS), showing that the Open Access (OA) articles were more cited than the non-OA ones....However, I [take issue with the statement that] "solid evidence to support or refute...that papers freely available in a journal will be more often read and cited than those behind a subscription barrier...has been surprisingly hard to find." The online bibliography, The effect of open access and downloads ('hits') on citation impact, records a growing number of studies reporting precisely such evidence as of 2001, including studies based on data from much larger samples of journals, disciplines and years than the PLoS study on PNAS --and they all find exactly the same effect: freely available articles are read and cited more....
In fact, the only new knowledge from this small, journal-specific sample was (1) the welcome finding of how early the OA advantage can manifest itself, plus (2) some less clear findings about differences between first- and last-author OA practices, plus (3) a controversial finding that will most definitely need to be replicated on far larger samples in order to be credible: "The analysis revealed that self- archived articles are also cited less often than OA articles from the same journal." The latter (3) is a...one journal (PNAS)...finding; the overwhelming majority of self-archived OA...articles today...do not appear in journals with a paid-OA option. Hence on the present evidence I have great difficulty in seeing this secondary advantage as any more than a paid-OA publisher’s pipe-dream at this point.
The following, however, is not a pipe-dream, but a peccadillo: "no other study has compared OA and non-OA articles from the same journal."...[I]t has to be stated that of [the] "potentially confounding" variables [Eysenbach identifies]...many are peculiar to this particular short-interval...single-journal PLoS study. And several of them (country, subject, year) had already been analyzed in papers that had been published before this 2006 article and were not taken into account despite the fact that both their preprints and their postprints had been freely accessible since well before publication, and that at least one of them (Brody et al. 2005) had been explicitly drawn to the author’s attention based on a preprint draft well before the article was submitted to PLoS. Brody et al. (2005) had found that, alongside the OA citation advantage, more downloads in the first six months after publication are correlated with more citations 18 months later in physics; and Hajjem et al. (2005) had found higher citations for OA articles --comparing always within the very same journal and year-- for 1,307,038 articles published across 12 years (1992-2003) in 10 disciplines (Biology, Psychology, Sociology, Health, Political Science, Economics, Education, Law, Business, Management).
Stevan's comment has also been published as a letter to the editor in PLoS Biology.
The open access movement:
Putting peer-reviewed scientific and scholarly literature
on the internet. Making it available free of charge and
free of most copyright and licensing restrictions.
Removing the barriers to serious research.
I recommend the OA tracking project (OATP) as the best way to stay on top of new OA developments. You can read the OATP feed on a blog-like web page or subscribe to it by RSS, email, or Twitter. You can also help build the feed by tagging new developments you encounter.
