5 However the slow growth in capital per worker has been quantitatively less important – accounting for only one-fourth of the slowdown in productivity compared with its long-run average – than the decline in the growth rate of total factor productivity (TFP), the portion of productivity that is not accounted for by measurable inputs to production.
Indeed, TFP growth has averaged less than 1/2 percent per year in the past 10 years, well below its long-run average of 1–1/4 percent. Pinning down the exact causes of this slowdown is difficult, and there are many possibilities.