Before revision:  We formalize this `irrelevance hypothesis ' using a dynamic stochastic general equilibrium model with UMP and test it empirically for  the United States and Japan using a structural vector autoregressive model that includes variables subject to occasionally binding constraints. The hypothesis is strongly rejected for both countries. However, a comparison of the impulse responses to a monetary policy shock across regimes shows that UMP has had strong delayed effects in each country .
After revision:  We formalize this `irrelevance hypothesis ' using a dynamic stochastic general equilibrium model with UMP and test it empirically for the United States and Japan using a structural vector autoregressive model with the ELB. For each country, we firmly reject the hypothesis but find that UMP has had strong delayed effects in each country .