Heather Morrison has published "Dramatic Growth of Open Access 2015 First Quarter" in The Imaginary Journal of Poetic Economics.
Here's an excerpt:
OpenDOAR added 129 repositories for a total of 2,857. The Bielefeld Academic Search Engine added close to 3 million documents for a total of over 71 million documents. Another 7,690 authors joined the Social Sciences Research Network for a total of over 275,000 authors.