“Are Open Access Monographs Discoverable in Library Catalogs?”, Libraries and the Academy, Volume 17, No. 1, January 2017…

The analysis indicates that only a small percentage of college and university library catalogs in the United States and Canada consistently enable discovery and access for the test sample.

“The open access aggregators challenge: how well do they identify free full text?”, Medium article-post, 7th January 2017. Looks at BASE and CORE…

when OAI-PMH (which is the standard way of harvesting open access repositories [was established,] no provision was made to have a standard way or a mandatory field to indicate if the item is free to access.” [But today] “many have in fact more metadata-only records than full-text records.

[BASE] “is only able to see 75 free records in National University of Singapore’s IR, 654 free records in Nanyang Technology University’s IR, 143 free records in Singapore Management University’s IR. I did not do a check to see if there were false positives in BASE’s identification of full text but [assuming] they are 100% correct, we see only a full text identification ratio of 0.6%, 3.8% and 2.7% respectively!” […] “the results for CORE are as dismal as BASE.

See also: “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 …