Working Paper: NBER ID: w20445
Authors: Anna Orlik; Laura Veldkamp
Abstract: A fruitful emerging literature reveals that shocks to uncertainty can explain asset returns, business cycles and financial crises. The literature equates uncertainty shocks with changes in the variance of an innovation whose distribution is common knowledge. But how do such shocks arise? This paper argues that people do not know the true distribution of macroeconomic outcomes. Like Bayesian econometricians, they estimate a distribution. Using real-time GDP data, we measure uncertainty as the conditional standard deviation of GDP growth, which captures uncertainty about the distributions estimated parameters. When the forecasting model admits only normally-distributed outcomes, we find small, acyclical changes in uncertainty. But when agents can also estimate parameters that regulate skewness, uncertainty fluctuations become large and counter-cyclical. The reason is that small changes in estimated skewness whip around probabilities of unobserved tail events (black swans). The resulting forecasts resemble those of professional forecasters. Our uncertainty estimates reveal that revisions in parameter estimates, especially those that affect the risk of a black swan, explain most of the shocks to uncertainty.
Keywords: uncertainty shocks; black swans; GDP growth; parameter uncertainty; skewness
JEL Codes: C53; E17; E44; G01; G14
Edges that are evidenced by causal inference methods are in orange, and the rest are in light blue.
| Cause | Effect |
|---|---|
| parameter uncertainty + skewness (C46) | fluctuations in uncertainty (E32) |
| changes in skewness (C46) | conditional variance of forecasts (C53) |
| economic downturns (F44) | increase in uncertainty (D89) |
| parameter estimation regulating skewness (C51) | fluctuations in uncertainty (E32) |
| negative skewness + parameter uncertainty (C46) | biases in professional forecasts (C53) |
| model predictions of uncertainty (C59) | observed economic phenomena (E39) |