Open Access Citation Advantage: An Annotated Bibliography
Though this question is not settled, the bibliography cites a number of studies designed to test the hypothesis of confounding extraneous causes. It is clear that open access articles are downloaded far more than toll access articles. Studies indicate this download advantage is easily 100% over toll access articles. It seems unlikely such a large download advantage would not to some degree eventually influence the number of citations. Studies typically show a 25-250% OACA or more. The higher end of that range might prove illusionary. However, even if the true OACA turns out to be only 10-15%, this would still be a major incentive for scholars to choose an open access publishing option. Note that many studies showed an OA advantage merely by reserving the right to mount their preprint or postprint to a repository or web site. Publication in an open access journal (Gold OA) apparently is not required to get a significant OA citation advantage.
From feeds:Open Access Tracking Project (OATP) » Connotea Imports
Open Access Tracking Project (OATP) » Amsciforum