[Openaccess] Evidence-based research on Open Access needed

Dear all, James Heilman, a doctor and Wikipedian, has been trying to convince the World Health Organization to go to a CC BY SA license for a few years now.

The Director of Knowledge, Ethics and Research at WHO stated: https://dgroups.org/hifa2015/discussions/35152a41

We would welcome sharing with us some evidence-based research on how licensing works under the Creative Commons attribution licence has made an impact in the area of scientific, technical and medical publishing.

Can we help James finding some sources and references for this? It's important.

Aubrey