Mankiw argued that Obama's GDP forecasts are too rosy. DeLong countered:

Whether an unexpected fall in production is followed by faster than average catch-up growth depends what kind the fall in production is. A fall in production that does not also change the unemployment rate will in all likelihood be permanent. A fall in production that is accompanied by a big rise in the unemployment rate will in all likelihood be reversed.

Krugman piles on. Mankiw wants to bet.

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