Since World War II,

Since World War II, the average recession in the United States has lasted 11 months. The longest recession in that time was 18 months, and the shortest was six. If you believe, like some economists do, that the current recession began in March, and that this is bound to be one of the worst in a long time -- because it combines the burst of the technology bubble and the shock of September 11 -- then we may have another nine months to go.

If you're interested, the history of US business contractions (and expansions) is worth a look. (Hint: the "trough from previous peak" column refers to recession length in months.)