We investigate the sources of the important shifts in the volatility of US macroeconomic variables in the postwar period. To this end, we propose the estimation of DSGE models allowing for time variation in the volatility of the structural innovations. We apply our estimation strategy to a large-scale model of the business cycle and find that shocks specific to the equilibrium condition of investment account for most of the sharp decline in volatility of the last two decades.

We estimate a state-of-the-art DSGE model to study the natural rate of interest in the United States over the last 20 years. The natural rate is highly procyclical, and fell substantially below zero in each of the last three recessions. Although the drop was of comparable magnitude across the three recessions, the decline was considerably more persistent in the Great Recession. We discuss the usefulness and limitations, particularly due to the zero lower bound, of the natural rate for the conduct of monetary policy.

The surge in credit and house prices that preceded the Great Recession was particularly pronounced in ZIP codes with a higher fraction of subprime borrowers We present a simple model with prime and subprime borrowers distributed across geographic locations, which can reproduce this stylized fact as a result of an expansion in the supply of credit. Due to their low income, subprime households are constrained in their ability to meet interest payments and hence sustain debt. As a result, when the supply of credit increases and interest rates fall, they take on disproportionately more debt than their prime counterparts, who are not subject to that constraint.