Proportion of Open Access Peer-Reviewed Papers at the European and World Levels—2004-2011 :
“This report re-assesses the Open Access (OA) availability of scholarly publications during the 2004 to 2011 period, for 22 fields of knowledge, as well as for the European Research Area countries, Brazil, Canada, Japan, and the US. Using a strategy to increase the number of free articles retrieved (that is, which aims to increasing recall), led to close to a doubling of the proportion of OA estimated by teams lead by Björk and by Harnad. The present report shows that the tipping point for OA (more than 50% of the papers available for free) has been reached in several countries, including Brazil, Switzerland, the Netherlands, the US, as well as in biomedical research, biology, and mathematics and statistics.”
URL : http://www.science-metrix.com/pdf/SM_EC_OA_Availability_2004-2011.pdf