Incertitude sur l'effet global ou sur les délais d'action de la politique monétaire : politique robuste et activisme

We compare two cases of uncertainty which have led to traditional arguments for less activist monetary policies: One, where the uncertainty concerns the global effect of policy, as in Brainard (1967); and the other where the uncertainty is about the the lags, as in Friedman (1960). We show that a bayesian approach leads to similar results in both cases, but that it is only in the case of uncertainty about lags that an approach in terms of robustness (through a minimax criterion) necessarily leads to less activism. Moreover, in that case, the robust policy is even less activist than what a bayesian approach would give. JEL Classification: E50, E60, D81.