A note on Fama

He has pointed out that recessions happen and cause disruptions. So obviously, during a crash his three factor model of stocks would fail, which it did. His three factor model begins to work again when GDP stabilizes.  How do I know this? Fama uses a regression analysis which requires a stable GDP trend before the coefficients stabilize. That in turn leads to a different conclusion.  Savings does not equal investment until GDP stabilize.  Krugman is right on this point.