  We propose a public goods game model of user sharing in an online commenting
forum. In particular, we assume that users who share personal information incur
an information cost but reap the benefits of a more extensive social
interaction. Freeloaders benefit from the same social interaction but do not
share personal information. The resulting public goods structure is analyzed
both theoretically and empirically. In particular, we show that the proposed
game always possesses equilibria and we give sufficient conditions for pure
strategy equilibria to emerge. These correspond to users who always behave the
same way, either sharing or hiding personal information. We present an
empirical analysis of a relevant data set, showing that our model parameters
can be fit and that the proposed model has better explanatory power than a
corresponding null (linear) model of behavior.
