Forum Size and Content Contribution per Person: A Field Experiment

Promoting contribution of content is a key challenge for platforms that support the collective creation or transfer of knowledge. We use a field experiment on a massive open online course to study the role of forum size (number of people in a forum) in the contribution of content per person. We find that larger forums elicit more contributions per person. The number of questions and other help-seeking threads posted per person was unchanged by forum size, but replies and other more conversational posts increased sharply. Most of the positive effect of size was in a subset of socially responsive subjects. The implication of social responsiveness driving our results is that the unequal distribution of contribution in online platforms is unlikely to be easily changed: if more contributions are elicited from infrequent contributors, the greatest contributors would contribute even more because there would be more to respond to.