Because the federal funds rate is the real rate plus the expected rate of inflation and because it is the real rate that influences economic activity, the amount of monetary accommodation represented by a given nominal level of the federal funds rate decreases as expected inflation declines.
In  11  Population growth has also moved gradually lower in the United States, though the effect has not been as large as in some foreign economies, where the size of the population is now stagnant or falling. 12  It is unclear how persistent recent low rates of measured productivity growth will be.