Initial Margin Requirements and Stock Returns Volatility: Another Look

Abstract

This article investigates the relationship between initial margin requirements and stock return volatility. Volatility is measured using a GARCH in Mean model. We find no evidence of an empirical relationship between margin requirements and the volatility of the S&P 500 index portfolio's excess returns. Evidence from short-sale data, and model sensitivity analysis are presented which support the hypothesis of no margin-volatility relationship. The results are consistent with the intertemporal CAPM model of Merton (1973) with an aggregate relative risk aversion measure of 4.1. In addition, we find evidence of long-term memory in conditional return distributions' volatility.