Laakso & Björk (2013)<http://hanken.halvi.helsinki.fi/portal/files/1311951/laakso_bj_rk_delay_preprint.pdf> compare the citation impact of immediate Gold OA with delayed Gold and toll-access. They find that delayed-Gold journals average twice as many citations per article as toll-access journals and three times as many as immediate-Gold journals.
This is based on comparisons between different journals. But journals differ in both subject matter and quality -- and one of the ways to try to equate them to make them comparable for quality is to equate them for impact. So if journals are not equated for subject matter and quality, one is comparing apples and oranges. But if immediate Gold OA, delayed-Gold and toll-access journals are equated for impact, one can't compare impact for delayed vs. immediate Gold -- in fact one can't compare the journals for citation impact at al!! A feasible way to compare immediate-OA with delayed-access and toll-access is via Green OA based on within-journal instead of between-journal comparisons, by comparing articles published within the same journal and year. To do this one needs both the date of publication and the date the article was made Green OA. It is impossible to get the OA date for webwide deposits in general, but for repository deposits it is possible. We do have some very preliminary and partial data<http://eprints.soton.ac.uk/358882/> from the University of Minho repository, but the sample is still too small to do within-journal comparisons. Immediate Green OA articles do have more citations on average than Delayed Access articles (see Figures 2c and 3c) despite the availability of the automated "Almost-OA" Button during the delay period, but these citation counts are just absolute ones, rather than relative to within-journal matched toll-access controls. Hence these are likewise still comparisons between apples and oranges. (Note also that the large number of undeposited articles is likewise unmatched, and not based on their respective within-journal matched toll-access controls.) The sample will grow as the number of Green OA mandates and repository deposits worldwide grows. The vast unused potential for immediate Green-OA and Almost-OA has long been known and noted -- most recently by Laakso (2014)<http://hanken.halvi.helsinki.fi/portal/files/2323707/Lakso_2014_Green_OA_Policies_Accepted_Version_.pdf> . Gargouri, Yassine, Larivière, Vincent & Harnad, Stevan (2013) Ten-year Analysis of University of Minho Green OA Self-Archiving Mandate<http://eprints.soton.ac.uk/358882/> (in E Rodrigues, Ed. *title to come)* Laakso, M., & Björk, B. C. (2013). Delayed open access: An overlooked high-impact category of openly available scientific literature<http://hanken.halvi.helsinki.fi/portal/files/1311951/laakso_bj_rk_delay_preprint.pdf> . *Journal of the American Society for Information Science and Technology*. Laakso, M (2014) Green open access policies of scholarly journal publishers: a study of what, when, and where self-archiving is allowed<http://hanken.halvi.helsinki.fi/portal/files/2323707/Lakso_2014_Green_OA_Policies_Accepted_Version_.pdf>. Scientometrics (in press)
_______________________________________________ GOAL mailing list GOAL@eprints.org http://mailman.ecs.soton.ac.uk/mailman/listinfo/goal
