...our sample contains 209 stock-market crashes and 59 depressions, with 41 matched by timing. In this context, the probability of a minor depression, contingent on seeing a stock-market crash, is 20%, and the corresponding chance of a major depression is only 2%. However, it is still the case that depressions are very likely to feature stock-market crashes -- 69% for minor depressions and 83% for major ones.
In the end, we learned two things. Periods without stock-market crashes are very safe, in the sense that depressions are extremely unlikely. However, periods experiencing stock-market crashes, such as 2008-09 in the U.S., represent a serious threat. The odds are roughly one-in-five that the current recession will snowball into the macroeconomic decline of 10% or more that is the hallmark of a depression.
The bright side of a 20% depression probability is the 80% chance of avoiding a depression. The U.S. had stock-market crashes in 2000-02 (by 42%) and 1973-74 (49%) and, in each case, experienced only mild recessions. Hence, if we are lucky, the current downturn will also be moderate, though likely worse than the other U.S. post-World War II recessions, including 1982.
In this relatively favorable scenario, we may follow the path recently sketched by Federal Reserve Chairman Ben Bernanke, with the economy recovering by 2010. On the other hand, the 59 nonwar depressions in our sample have an average duration of nearly four years, which, if we have one here, means that it is likely recovery would not be substantial until 2012.
Given our situation, it is right that radical government policies should be considered if they promise to lower the probability and likely size of a depression. However, many governmental actions -- including several pursued by Franklin Roosevelt during the Great Depression -- can make things worse.
I wish I could be confident that the array of U.S. policies already in place and those likely forthcoming will be helpful. But I think it more likely that the economy will eventually recover despite these policies, rather than because of them.