Stock Market Crashes and Depressions
A new study at the NBER.
Long-term data for 25 countries up to 2006 reveal 195 stock-market
crashes (multi-year real returns of -25% or less) and 84 depressions
(multi-year macroeconomic declines of 10% or more), with 58 of the
cases matched by timing. The United States has two of the matched
events--the Great Depression 1929-33 and the post-WWI years 1917-21,
likely driven by the Great Influenza Epidemic. 45% of the matched cases
are associated with war, and the two world wars are prominent.
Conditional on a stock-market crash, the probability of a minor
depression (macroeconomic decline of at least 10%) is 30% and of a
major depression (at least 25%) is 11%. In a non-war environment, these
probabilities are lower but still substantial--20% for a minor
depression and 3% for a major depression. Thus, the stock-market
crashes of 2008-09 in the United States and other countries provide
ample reason for concern about depression. In reverse, the probability
of a stock-market crash is 69%, conditional on a depression of 10% or
more, and 91% for 25% or more. Thus, the largest depressions are
particularly likely to be accompanied by stock-market crashes, and this
finding applies equally to non-war and war events. We allow for
flexible timing between stock-market crashes and depressions for the 58
matched cases to compute the covariance between stock returns and an
asset-pricing factor, which depends on the proportionate decline of
consumption during a depression. If we assume a coefficient of relative
risk aversion around 3.5, this covariance is large enough to account in
a familiar looking asset-pricing formula for the observed average
(levered) equity premium of 7% per year. This finding complements
previous analyses that were based on the probability and size
distribution of macroeconomic disasters but did not consider explicitly
the covariance between macroeconomic declines and stock returns.
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