This is the most thorough summary of MOOC completion rate data that I have seen – for xMOOCs. Kudos to Katy for putting together this data, and please comment on her blog post to let her know of new data available.
The problem I see is that scalar metrics of # of students and completion rates are insufficient for open courses, where there are different student types. Only a subset of students actually plan to complete a course, whereas the majority of students enrolled are there only to sample and explore. Measuring completion rate off the total number of students is misleading, but so is touting the total number of students enrolled (billions served) as a key metric.
Read more at: http://mfeldstein.com/the-most-thorough-summary-to-date-of-mooc-completion-rates/