This paper estimates a New Keynesian model of the U.S. economy over the period following the 2001 slump, a period for which the adequacy of monetary policy is intensely debated. To relate to this debate, we consider alternative in ‡ation series in the estimation. We ...nd that only when measuring in ‡ation with core PCE monetary policy appears to have been reasonable and su¢ciently active to rule out indeterminacy. We then relax the assumption that in ‡ation in the model is measured by a single

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... indicator and re-formulate the arti...cial economy as a factor model where the theory's concept of in ‡ation is the common factor to the empirical in ‡ation series. We ...nd that CPI and PCE provide better indicators of the latent concept while core PCE is less informative. Finally, we allow for positive trend in ‡ation and the emerging results complement our previous ...ndings. Again, even with these extensions, the only instance in which we can con...dently rule out indeterminacy is when we measure in ‡ation with core PCE. JEL codes E32, E52, E58.