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AbstractA casual inspection of a graph of volatility indexes over time indicates that volatility has undergone infrequent, but significant, shifts in its average level. The purpose of this article is to test for multiple structural breaks in the mean level of market volatility measured by the VIX and VXO, and to identify statistically the dates of these mean shifts. We find evidence of three distinct periods: pre‐1992, 1992–1997, and post‐1997. We find that the mean volatility, as well as its standard deviation, was lowest during 1992–1997. Our findings provide statistical evidence consistent with popular beliefs that market volatility changes over time.

I study how a revolutionary vanguard might use violence to mobilize a mass public. The mechanism is informational—the vanguard uses violence to manipulate population member's beliefs about the level of antigovernment sentiment in society. The model has multiple equilibria, one equilibrium in which there may be revolution and another in which there is certain not to be. In the former, structural factors influence expected mobilization, whereas in the latter they do not. Hence, the model is consistent with structural factors influencing the likelihood of revolution in some societies but not others, offering a partial defense of structural accounts from common critiques. The model also challenges standard arguments about the role of revolutionary vanguards. The model is consistent with vanguard violence facilitating mobilization and even sparking spontaneous uprisings. However, it also predicts selection effects—an active vanguard emerges only in societies that are already coordinated on a participatory equilibrium. Hence, a correlation between vanguard activity and mass mobilization may not constitute evidence for the causal efficacy of vanguards—be it through creating focal points, providing selective incentives, or communicating information.