Self-­Selected or Mandated, Open Access Increases Citation Impact for Higher Quality Research

Abstract:

Background: Articles whose authors have supplemented subscription-based access to the publisher’s version by self-archiving their own final draft to make it accessible free for all on the web (“Open Access”, OA) average twice as many citations as articles in the same journal and year that have not been made OA. Some have suggested that this “OA Advantage” may not be causal but just a self-selection bias, because authors preferentially make higher-quality articles OA. To test this we compared self-selective self-archiving with mandatory self-archiving for a sample of 27,197 articles published
2002-2006 in 1,984 journals.

Methdology/Principal Findings: The OA Advantage proved just as high for both. Logistic regression analysis showed that the advantage is independent of other correlates of citations (article age; journal impact factor; number of co-authors, references or pages; field; article type; or country) and greatest for the most highly cited articles. The OA Advantage is real, independent and causal, but skewed. Its size is indeed correlated with quality, just as citations themselves are (the top 20% of articles receive about 80% of all citations).

Conclusions/Significance: The OA advantage is greater for the more citable articles, not because of a quality bias from  authors self-selecting what to make OA, but because of a quality advantage, from users self-selecting what to use and cite, freed by OA from the constraints of selective accessibility to subscribers only. It is hoped that these findings will help motivate the adoption of OA self-archiving mandates by universities, research institutions and research funders.

One-sentence Summary: We demonstrate that the greater citation impact of open access research is causal rather than an artifact of author bias (i.e., authors self-selectively making higher quality research open access) by showing that the citation increase is just as great when the open access is mandatory; the open access impact advantage is independent of other correlates of citation impact, and greater for higher quality research.