Group Size and Incentive to Contribute: A Natural Experiment at Chinese Wikipedia

The literature of private provision of public goods suggests that incentive to contribute is inversely related to group size. This paper empirically tests this relationship using field data from Chinese Wikipedia, an online encyclopedia. We exploit an exogenous reduction in group size as a result of the blocking of Wikipedia in mainland China and examine whether individual contributions increase after the block as predicted in the literature. Our result indicates the opposite: individual contribution of unaffected contributors decreases by 42% on average as a result of the block. We attribute the cause to social effects: contributors care about the number of beneficiaries of their contributions. We build a simple model to illustrate how social effects and group size affect individual incentive to contribute. Consistent with our model prediction, we find that the more a contributor values social recognition, the greater the reduction in her contributions after the block. A series of robustness checks appear to support our explanation.