Unpredictable rainfall is an important risk for agricultural activity, and farmers in developing countries often receive incomplete insurance from informal risk-sharing networks. We study the demand for, and effects of, offering formal index-based rainfall insurance through a randomized experiment in an environment where the informal risk sharing network can be readily identified and richly characterized: sub-castes in rural India. A model allowing for both idiosyncratic and aggregate risk shows that informal networks lower the demand for formal insurance only if the network indemnifies against aggregate risk, but not if its primary role is to insure against farmer-specific losses. When formal insurance carries basis risk (mismatches between payouts and... |