Though Mass Open Online Courses are very different from each other in their structure, content or audience, they are all characterized by low completion rates. In this paper, we use the Cox proportional hazard model to analyze student retention in the MOOC Principle of Microeconomics. Using two different measures of retention, video watching and quiz submission, we show that students’ commitment to the course can be strongly predicted by their participation in the first week’s activities. Data collected through a voluntary opt-in survey allow us to study retention in relation to demographics, for a subset of enrollees. We find a higher dropout rate for college students or younger participants. Female attrition is larger when measured by video watching but not when measured by quiz completion. Self-ascribed motivation for taking the course is not a predictor of completion. We conclude that raw completion rates cannot be the criterion to judge the success of MOOCs, as it is in case of traditional courses. The results are consistent with the existing literature which separates MOOCs students into two different groups: Committed Learners and Browsers.