(1) says that:
In 2012, the worldwide amount of digital health care data was estimated to be around 500 petabytes, expected to reach 25,000 petabytes in 2020, of which approximately 80% is unstructured.
What fraction of it is openly accessible?
(1) Van Poucke S, Thomeer M, Heath J, Vukicevic M Are Randomized Controlled Trials the (G)old Standard? From Clinical Intelligence to Prescriptive Analytics J Med Internet Res 2016;18(7):e185 URL: http://www.jmir.org/2016/7/e185 DOI: 10.2196/jmir.5549 PMID: 27383622