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.
While weak investment levels, particularly early on in the recovery, likely contributed to lower productivity gains, investment levels going forward could be closer to historical norms. Also, recent technological gains may eventually contribute strongly to productivity growth; see, for example, Baily, Manyika, and Gupta (2013).