Ass Professor Laura Czerniewicz of the University of Cape Town recently asked about the percentage of scholarly peer-reviewed journals that are now open access. In brief, my response is "about 30%" (apparently Heather Joseph from SPARC gave almost exactly the same response). This figure needs to be taken with a huge grain of salt, though. My full response illustrates why:
Any such figure would be a very rough ballpark, because we don't have a count of how many peer-reviewed journals there are in the world. We tend to use Ulrich's as a surrogate, however this list reflects a strong English-language / western bias, e.g. Ulrich's would only include a very
tiny fraction of the academic journals from China.
Something else to keep in mind is that is has become more difficult to assess the number of peer-reviewed journals in Ulrich's, because the default search does not deduplicate for multiple formats (i.e. a quick search for academic / peer-reviewed / scholarly journals will yield two titles when a journal is produced in both print and electronic form).
My latest count of active, peer-reviewed scholarly journals from Ulrich's using deduplication from Dec. 1, 2011 is 26,746. My method and calculations are shown here, in this appendix of my draft thesis:
If we take the DOAJ current figure of 7,665 journals as the number of OA journals, this gives a rough guesstimate of 28% of scholarly peer-reviewed journals that are fully open access. I would like to
emphasize that these numbers need to be taken with a grain of salt - my Ulrich's deduplication exercise is a quick and dirty one, and not all OA journals are necessarily in DOAJ (e.g. there is generally a delay in adding titles due to the vetting process).