Knoth, Petr (2013). “From open access metadata to open access content: two principles for increased visibility of open access content”, conference paper presented at: Open Repositories 2013, 8th-12th July 2013, Charlottetown, Canada.

… only 27.6% of research outputs in repositories are linked to content that can be downloaded by automatic means and analysed (e.g. indexed). […] the median repository will only provide machine readable content for 13% of its deposited resources. [but] it is likely that these statistics are in fact rather optimistic …