The OA advantage is real

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

http://arxiv.org/abs/1001.0361

Yassine Gargouri, Chawki Hajjem, Vincent Lariviere, Yves Gingras, Les
Carr, Tim Brody, Stevan Harnad

ABSTRACT: Articles whose authors make them Open Access (OA) by
self-archiving them online are cited significantly more than articles
accessible only to subscribers. 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. The OA Advantage proved just as high for both.
Logistic regression 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). The advantage is greater for the
more citeable 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.