Free access means that non-scientists can read articles, and most non-scientists will not cite them. The problem is that there is no feedback path for normal people to critique articles.
There is a methodological flaw. People who cite articles either work in institutions that have an esubscription to a journal or not. Those that do not are not likely to check its contents since they will not be able to read any of its articles behind its paywall so they will not be able to take opportunity of the occasional free article since they will not know about it, those with access will not notice the difference between free and nonfree.
Many studies have reported a significant increase in citations for articles whose authors make them OA by self-archiving them. To show that this citation advantage is not causal but just a self-selection artifact (because authors selectively self-archive their better, more citeable papers), you first have to replicate the advantage for the self-archived OA articles in your sample, and then show that the advantage is absent for the articles made OA at random. Davis showed only that the citation advantage was absent altogether in his sample. The likely reason is that the sample was much too small (36 journals, 712 articles randomly OA, 65 self-archived OA, 2533 non-OA). Gargouri et al 2010 controlled for self-selection with mandated (obligatory) OA rather than random OA. The far larger sample (1984 journals, 3055 articles mandatorily OA, 3664 self-archived OA, 20,982 non-OA) found a significant citation advantage of about the same size for both self-selected and mandated OA.
ereneon
Mar 30, 2011