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

The literature of private provision of public goods suggests thatincentive to contribute is inversely related to group size. This paperempirically tests this relationship using field data from ChineseWikipedia, an online encyclopedia. We exploit an exogenous reduction ingroup size as a result of the blocking of Wikipedia in mainland Chinaand examine whether individual contributions increase after the block aspredicted in the literature. Our result indicates the opposite:individual contribution of unaffected contributors decreases by 42% onaverage as a result of the block. We attribute the cause to socialeffects: contributors care about the number of beneficiaries of theircontributions. We build a simple model to illustrate how social effectsand group size affect individual incentive to contribute. Consistentwith our model prediction, we find that the more a contributor valuessocial recognition, the greater the reduction in her contributions afterthe block. A series of robustness checks appear to support our explanation.