Econometric studies of the effects of research on productivity have typically imposed arbitrary restrictions on the length and shape of the R&D on productivity and the estimated rate of return to research. This paper argues that the useful stock of public knowledge depreciates, if at all, only...

Econometric studies of the effects of research on productivity have typically imposed arbitrary restrictions on the length and shape of the R&D lag profile. These restrictions are likely to have biased up both the measured effects of R&D on productivity and the estimated rates of return to...