The views expressed are those of the authors and do not necessarily reflect official positions of the Federal Reserve Bank of St. Louis, the Federal Reserve System, the Board of Governors, or the National Bureau of Economic Research. We thank Dean Corbae and Pablo D'Erasmo for sharing data on corporate defaults. At least one co-author has disclosed a financial relationship of potential relevance for this research. Further information is available online at http://www.nber.org/papers/w27439.ack NBER working papers are circulated for discussion and comment purposes. They have not been peer-reviewed or been subject to the review by the NBER Board of Directors that accompanies official NBER publications.

The "Great Recession" was a deep downturn with long-lasting effects on credit markets, labor markets and output. We explore a simple explanation: This recession has been more persistent than others because it was perceived as an extremely unlikely event before2007. Observing such an episode led all agents to re-assess macro risk, in particular, the probability of tail events. Since changes in beliefs endure long after the event itself has passed and through its effects on prices and choices, it produces long-lasting effects on investment, employment and output. To model this idea, we study a production economy with agents who use standard econometric tools to estimate the distribution of aggregate shocks. When they observe a new shock, they re-estimate the distribution from which it was drawn. Even transitory shocks have persistent effects because, once observed, they stay forever in the agents' data set. We feed a time-series of US macro data into our model and show that our belief revision mechanism can explain the 12% downward shift in US trend output.JEL Classifications: D84, E32

The Great Recession was a deep downturn with long-lasting effects on credit, employment and output. While narratives about its causes abound, the persistence of GDP below pre-crisis trends remains puzzling. We propose a simple persistence mechanism that can be quantified and combined with existing models. Our key premise is that agents don't know the true distribution of shocks, but use data to estimate it non-parametrically. Then, transitory events, especially extreme ones, generate persistent changes in beliefs and macro outcomes. Embedding this mechanism in a neoclassical model, we find that it endogenously generates persistent drops in economic activity after tail events.

The Great Recession was a deep downturn with long-lasting effects on credit, employment and output. While narratives about its causes abound, the persistence of GDP below pre-crisis trends remains puzzling. We propose a simple persistence mechanism that can be quantfied and combined with existing models. Our key premise is that agents don't know the true distribution of shocks, but use data to estimate it non-parametrically. Then, transitory events, especially extreme ones, generate persistent changes in beliefs and macro outcomes. Embedding this mechanism in a neoclassical model, we find that it endogenously generates persistent drops in economic activity after tail events.

We thank Jonathan Parker, Marty Eichenbaum and Mark Gertler for helpful comments and suggestions. The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research. At least one co-author has disclosed a financial relationship of potential relevance for this research. Further information is available online at http://www.nber.org/papers/w24362.ack NBER working papers are circulated for discussion and comment purposes. They have not been peer-reviewed or been subject to the review by the NBER Board of Directors that accompanies official NBER publications.