Open and Shut?: The NIH Public Access Policy: A triumph of green open access?

"... let’s consider the National Institutes of Health (NIH) Public Access Policy. This is described on Wikipedia as an 'open access mandate', and by Nature as a green OA policy, since it requires that all papers published as a result of NIH funding have to be made freely available in the NIH repository PubMed Central (PMC) within 12 months of publication. In fact, the NIH policy is viewed as the premier green OA policy.

But how many of the papers being deposited in PMC in order to comply with the Policy have a CC BY licence attached and so are, strictly speaking, open access?"