 ** For a comprehensive annotated bibliography of studies up to 0000, including studies that do and do not support the OA citation advantage, see Steve Hitchcock, [http://opcit.eprints.org/oacitation-biblio.html The effect of open access and downloads ('hits') on citation impact: a bibliography of studies], OpCit Project. SPARC Europe continued Hitchcock's bibliography in its [http://sparceurope.org/what-we-do/open-access/sparc-europe-open-access-resources/open-access-citation-advantage-service-oaca/ Open Access Citation Advantage Service]