[ericd]

For people fully devoted to studying, and with some sort of extrinsic incentive to complete the courses, I imagine that the completion rate would be significantly higher. When I was at MIT, some of the courses worked almost exactly like MOOCs do now, and just as many people completed those as the traditional courses.

With MOOCs, a ton of the takers are not full-time students. I've taken some MOOC courses and only completed one (probabilistic graphical models). The main reason is that I have much higher priorities now, and the courses are on a strict schedule. The first time there's a choice between getting a piece of code finished that I need for a business deal done and finishing a problem set, that problem set is not getting finished.