Go here . His conclusion:
We badly want macroeconometrics to work. If it did, we could resolve bitter theoretical disputes with evidence. We could achieve better forecasting and control of the economy. Unfortunately, the world is not set up to enable macroeconometrics to work. Instead, all macroeconometric models are basically simulation models that use data for calibration purposes. People judge these models based on their priors for how the economy works. Imposing priors related to rational expectations does not change the fact that macroeconometrics provides no empirical information to anyone except those who happen to share all of the priors of the model-builder.