More is Less? The Effects of Multiple Group Membership on Information Generation: Evidence from an Online Maternity Community

Lingqing Jiang, Zhen Zhu


Social support from peers plays a positive and important role in many contexts. Today, the emergence of online social communities provides possibility to seek social support to maternity from other individuals that is complementary to those from the family and government. Our paper investigates the effects of multiple group membership on social support in terms of information generation in peer groups formed by pregnant women. Multiple group membership is increasingly common and its effects are of high interests in organisations. However, the fact that the decision of enrolling in multiple groups is endogenous makes it empirically challenging to identify causal effects. We use data from an online maternity community to investigate the effects of enrolling in multiple peer groups on information generation among about 27,000 pregnant women. The community allocates pregnant users---based on their estimated due date (EDD)---to default peer groups where they can exchange relevant information during pregnancy. We instrument the enrollment in additional peer groups by the day of users' EDD, which allows causal identification. We find evidence for substitution effects as well as spillover effects on users' information generation in their default peer group. The spillover effects, however, depend on the nature of the peer groups.

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