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Abstract
Many researchers and commentators underestimate the length and importance of the time lags
between initial research investment and ultimate impacts on the development and adoption of
technological innovations. In both econometric studies of productivity and ex post and ex ante
benefit-cost evaluations of research investments, researchers typically impose untested
assumptions about the R&D lag, which can have profound implications for the results. In this
paper we present a range of evidence on agricultural R&D lags including both aggregative
analysis of U.S. agricultural productivity using time series data, and some specific details on the
timelines for the research, development, and adoption processes for particular mechanical and
biological innovations in U.S. agriculture. The aggregative analysis makes use of a
comparatively rich state-level data set on U.S. agriculture that makes it possible to test
hypotheses about the R&D lag and to evaluate the implications for the specification of models of
production and for findings regarding the rate of return to public research investments. The
results support the use of a longer lag with a different shape than is typically imposed in studies
of industrial R&D. These findings are supported by the timelines for specific technological
innovations, including new crop varieties, as well as tractors and other mechanical innovations.