Are Ideas Really Getting Harder to Find?

Bloom et al. (2020) attribute the post-WWII slowdown in growth of U.S. TFP and other productivity measures to a decline in research productivity. A weakness in their approach is that the authors measure research productivity as the annual growth rate of industrial or economywide productivity divided by the number of researchers, contemporaneously. They give no consideration to the stock-flow relationships whereby current research effort gives rise to increments to a stock of depreciable knowledge and hence an evolving path of enhanced productivity over an extended but possibly finite future period. Using examples from agriculture, for which we have comparatively rich data, we revisit established ideas and evidence on links between research spending and productivity. On both conceptual and empirical grounds, we question whether the evidence supports the claim that a decline in productivity of researchers is responsible for the slowdown in productivity growth that has been observed, the large increases in numbers of scientists and in spending per scientist notwithstanding.