What are the odds of Depression?

Article by Harvard economics professor Robert Barro, writing in the Wall Street Journal, on a study of the odds of a Depression, given the stock market crash:

Central questions these days are how severe will the U.S. economic downturn be and how long will it last?

The most serious concern is that the downturn will become something worse than the largest recession of the post-World War II period -- 1982, when real per capita GDP fell by 3% and the unemployment rate peaked at nearly 11%. Could we even experience a depression (defined as a decline in per-person GDP or consumption by 10% or more)?

The U.S. macroeconomy has been so tame for so long that it's impossible to get an accurate reading about depression odds just from the U.S. data. My approach uses long-term data for many countries and takes into account the historical linkages between depressions and stock-market crashes. (The research is described in "Stock-Market Crashes and Depressions," a working paper Jose Ursua and I wrote for the National Bureau of Economic Research last month.)

The bottom line is that there is ample reason to worry about slipping into a depression. There is a roughly one-in-five chance that U.S. GDP and consumption will fall by 10% or more, something not seen since the early 1930s.

Our research classifies just two such U.S. events since 1870: the Great Depression from 1929 to 1933, with a macroeconomic decline by 25%, and the post-World War I years from 1917 to 1921, with a fall by 16%. We also assembled long-term data on GDP, consumption and stock-market returns for 33 other countries, sometimes going back as far as 1870. Our conjecture was that depressions would be closely connected to stock-market crashes (at least in the sense that a crash would signal a substantially increased chance of a depression). ...

Article here.