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From the QJE, by Alexandr Kopytov, Mathieu Taschereau-Dumouchel, and Zebang Xu:
We propose a tractable model in which risk, at both the micro and macro levels, is endogenous and driven by incentives. In the model, each firm chooses the mean and the variance of its productivity process, as well as how it covaries with the productivity of other firms. Aggregate risk arises when firms select productivity processes that are correlated with one another. The theory predicts that larger firms and those with lower markups are less volatile and less correlated with aggregate productivity. We find support for these predictions in the data. Through their impact on risk-taking decisions, distortions such as taxes and markups can make GDP more volatile in equilibrium. In a calibrated version of the model, removing distortions significantly reduces GDP volatility.
Fischer Black! (And my own earlier book Risk and Business Cycles). Via the excellent Kevin Lewis.
