The 2008 stock market crash destroyed $16.4 trillion of American households’ net worth from 2007 through 2009. Xavier Gabaix, a finance professor at New York University, has derived a crash-frequency formula that he believes captures a universal trait of all markets, not just equity markets or those in the U.S. According to that formula, the odds of a 12.8% crash in any given six-month period are 0.92%, almost as low as the actual frequency in the U.S. stock market over the last century.
Generally speaking, crashes usually occur under the following conditions: a prolonged period of rising stock prices and excessive economic optimism, a market where P/E ratios exceed long-term averages, and extensive use of margin debt and leverage by market participants.
Using survey data on households’ subjective probability beliefs about the one-year-ahead return on the Dow Jones stock market index, we estimated the effect of the stock market crash on the population average of expected returns, the population average of the uncertainty about returns (subjective standard deviation) and heterogeneity in expected returns.
Stock market risk increased dramatically, as indicated by the trend in volatility on Figure 1 Even those who do not follow the stock market could become more uncertain about the future of the economy in general and the stock market, in particular, as general uncertainty has been in the air” throughout the crisis.
We estimate the effect of the crash on the population average of expected returns, the population average of the uncertainty about returns (subjective standard deviation), and the cross-sectional heterogeneity in expected returns (an indicator of disagreement).