Group insurance and lending with endogenous social collateral

We construct a dynamic model of self-enforcing insurance provision and lending to a community of borrowers who are connected by risk-sharing arrangements that are themselves subject to enforcement problems, as in Kocherlakota (1996). We show that an outside lender offering constant-consumption contracts can earn a higher profit if he conditions his repeated interactions with each borrower on the history of his interactions with all the group members (a joint liability contract), rather than on his history with that borrower only (individual liability contracts). This result holds even in the absence of informational asymmetries. The observation driving it is that with individual liability contracts, a joint welfare-maximizing group may prefer to have one or more group members default on their contracts, so that the group can consume a mix of outside funds and the defaulters' stochastic income. One contribution of our work is to give precise economic content to the concept of "social collateral" as the per-agent surplus from group risk-sharing over autarky. The group can deter its members from defaulting on their contracts with the principal by threatening to reduce that surplus.