The shaded area in Figure 2 is the difference between the current zero-constrained level of the funds rate and the level recommended by the policy rule. It represents a monetary policy funds rate shortfall, that is, the desired amount of monetary policy stimulus from a lower funds rate that is unavailable because nominal interest rates can’t go below zero.This policy shortfall is sizable. Indeed, the Fed has been able to ease the funds rate only about half as much as the policy rule recommends.It is also persistent.According to the historical policy rule and FOMC economic forecasts, the funds rate should be near its zero lower bound not just for the next six or nine months, but for several years.The policy shortfall persists even though the economy is expected to start to grow later this year. Given the severe depth of the current recession, if will require several years of strong economic growth before most of the slack in the economy is eliminated and the recommended funds rate turns positive.