Higher initial margin requirements are associated with lower subsequent stock market volatility during normal and bull periods, but show no relationship during bear periods. Higher margins are also negatively related to the conditional mean of stock returns, apparently because they reduce systemic risk. We conclude that a prudential rule for setting margins (or other regulatory restrictions) is to lower them in sharply declining markets in order to enhance liquidity and avoid a depyramiding effect in stock prices, but subsequently raise them and keep them at the higher level in order to prevent a future pyramiding effect.

Higher initial margin requirements are associated with lower subsequent stock market volatility during normal and bull periods, but show no relationship during bear periods. Higher margins are also negatively related to the conditional mean of stock returns, apparently because they reduce systemic risk. We conclude that a prudential rule for setting margins (or other regulatory restrictions) is to lower them in sharply declining markets in order to enhance liquidity and avoid a depyramiding effect in stock prices, but subsequently raise them and keep them at the higher level in order to prevent a future pyramiding effect

We study an equilibrium risk and return model to explore the effects of the coronavirus crisis and associated skewness on the market price of risk. We derive the moment and equilibrium equations, specifying skewness price of risk as an additive component of the effect of variance on mean expected return. We estimate our model using the flexible skewed generalized error distribution, for which we derive the distribution of returns and the likelihood function. Using S&P 500 Index returns from January 1980 to mid-October 2020, our results show that the coronavirus crisis generated a deeply negative reaction in the skewness and total market price of risk, more negative even than the subprime and the October 1987 crises.