Learning with Rare Disasters
64 Pages Posted: 25 Jun 2019 Last revised: 5 Sep 2019
Date Written: September 5, 2019
Financial crises appear to have long-lasting effects, even after the crisis itself has past. This paper offers a simple explanation through Bayesian learning from rare events. Agents face a latent and time-varying probability of economic disaster. When a disaster occurs, learning results in greater effects on asset prices because agents update their probability of future disasters. Moreover, agents' belief that the disaster risk is high can rationally persist for years, even when it is in fact low. We generalize the model to allow for a noisy signal of the disaster probability. This generalized model explains excess stock market volatility together with negative skewness, effects that previous models in the literature struggle to explain.
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