Why Does Stock Market Volatility Change Over Time?

This paper analyzes the relation of stock volatility with real and nominal macroeconomic volatility, financial leverage, stock trading activity, default risk, and firm profitability using monthly data from 1857-1986. An important fact, previously noted by Officer [l973], is that stock return variability was unusually high during the 1929-1940 Great Depression. Moreover, leverage has a relatively small effect on stock volatility. The amplitude of the fluctuations in aggregate stock volatility is difficult to explain using simple models of stock valuation.