Is there too much or too little research and development (R&D)? In this paper we bridge the gap between the recent growth literature and the empirical productivity literature. We derive in a growth model the relationship between the social rate of return to R&D and the coefficient estimates of the empirical literature and show that these estimates represent a lower bound. Furthermore, our analytic framework provides a direct mapping from the rate of return to the degree of underinvestment in research. Conservative estimates suggest that optimal R&D investment is at least two to four times actual investment.

This paper comments on recent developments in the literature on the econometric analysis of international growth and convergence. It notes that panel estimates of the neoclassical model, accommodating level effects for individual countries through heterogeneous intercepts, deal with some of the econometric difficulties arising in some of the earlier cross-sectional studies. But it notes that, in dynamic panels, heterogeneity in growth effects and in speeds of convergence renders this estimator inconsistent also. The pervasiveness of such heterogeneity is demonstrated in three samples of countries, and the effects of (incorrectly) imposing homogeneity on estimated parameters are illustrated and discussed.