Open Access to Research Increases Citation Impact

We analyzed the effect of providing 'Open Access' (OA; free online access to research articles) on their 'citation impact' (how often they are cited). Using a subset of the ISI CD-ROM database from 1992 - 2003, we compared, within each journal and year, articles to which their authors had (OA) or had not (NOA) provided open access by self-archiving them on the web. The number of OA and NOA articles and their respective citation counts were calculated within biology, business, psychology and sociology journals. The percentage of OA articles varied from 5-20% (mean and median, 12%). The citation counts (OA-NOA/NOA) showed a consistent OA advantage (mean 96%, median 73%) for all four fields and 28 subspecialties tested, varying from 25% to over 250%. An OA impact advantage has already been reported in the physical sciences and engineering (physics, computer science), but there was uncertainty about whether the same thing happens in other disciplines. Our data now show that both the biological and the social sciences show the OA advantage, and are hence likewise losing substantial amounts of potential impact for the 80-95% of their articles that are not yet self-archived. These results confirm that a mandatory self-archiving policy on the part of research institutions and funders would greatly enhance the impact of research results in all disciplines