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...