Have individual stocks become more volatile? An empirical exploration of idiosyncratic risk

This article examines the volatility of common stocks at the market, firm and industry levels using a disaggregated approach. Results show an increase in the firm-level volatility from 1962-1997; the correlations between individual stocks and the market model's explanatory power has declined, while the number of stocks needed for diversification have increased; finally, market volatility leads the other volatility areas.