Thomas Eger et al. have self-archived "The Determinants of Open Access Publishing: Survey Evidence from Countries in the Mediterranean Open Access Network (MedOANet)."
Here's an excerpt:
We discuss the results of a survey conducted between April 2013 and May 2014 in six Mediterranean countries and covering 2,528 researchers from Spain (1,291), Portugal (142), France (380), Italy (596), Turkey (131) and Greece (130). We compare the results to our German survey with 1,913 respondents. We show that there are significant differences between the scientific disciplines with respect to researcher's awareness of and experience with both open access (OA) journals and self-archiving. Accordingly, the publishing culture (e.g. reputation, publishing language) but also other issues like age and certain policies (MedOANet) may explain why researchers make more frequent use of OA publishing in some countries and disciplines.