  Massive open online courses (MOOCs) promise to make rigorous higher education
accessible to everyone, but prior research has shown that registrants tend to
come from backgrounds of higher socioeconomic status. We study geographically
granular economic patterns in about 76,000 U.S. registrations for about 600
HarvardX and MITx courses between 2012 and 2018, identifying registrants'
locations using both IP geolocation and user-reported mailing addresses. By
either metric, we find higher registration rates among postal codes with
greater prosperity or population density. However, we also find evidence of
bias in IP geolocation: it makes greater errors, both geographically and
economically, for users from more economically distressed areas; it
disproportionately places users in prosperous areas; and it underestimates the
regressive pattern in MOOC registration. Researchers should use IP geolocation
in MOOC studies with care, and consider the possibility of similar economic
biases affecting its other academic, commercial, and legal uses.
