Björk BC, Welling P, Laakso M, et al. Open access to the scientific journal literature: situation 2009. PLoS One 2010;5:e11273. http://www.plosone.org/article/info:doi/10.1371/journal.pone.0011273
A survey published in PLoS ONE found that 1 in 5 research papers published in 2008 are currently available free online. Researchers at the Hanken School of Economics in Helsinki, Finland, checked the availability of 1837 randomly selected articles from the Scopus database (http://info.scopus.com). They found that 8.5% were freely available on the publishers' websites, with a further 11.9 percent available on authors' websites or in repositories. Earth sciences had the highest proportion of open-access (OA) articles (33%), while chemistry had the lowest (13%). In life sciences, most OA articles were 'gold' (free at publishers' websites), while in other disciplines, most OA articles were green (only available on authors' websites or in repositories).