To examine the severity of the zero bound problem, Reifschneider and Williams simulate the FRB/US model under alternative assumptions about the long-run inflation objective. In performing the simulations, the authors assume the shocks buffeting the model economy are similar in magnitude to those that have actually hit the U.S. economy in recent decades. Since the size of the shocks is not unusual in a historical perspective, the simulations can be used to judge the extent of the zero bound as a problem for economic stability.