Attribution and other problems in assessing the returns to agricultural R&D

Estimated rates of return to research are distorted by problems of attribut ing the credit for particular research results, or for particular research- induced productivity increases, among research expenditures undertaken at d ifferent times, in different places, and by different agencies. A comprehen sive assessment of the evidence from past economic evaluations of the retur ns to agricultural R&D indicates that studies generally report high rates o f return, with enormous variation among studies, but that much of this evid ence has been tainted by inadequate attention to attribution problems. This paper raises these concerns in a general way and illustrates their importa nce with reference to two particular types of attribution problem. First, w e consider the problem of accounting for locational spillovers in attributi ng varietal-improvement technology among research performers, using US whea t varieties as an example. Second, we consider the temporal aspects of the attribution problem using the specification of research lags in econometric models to illustrate the problem of attributing aggregate productivity gai ns to research expenditures made at different times. (C) 2001 Elsevier Scie nce B.V. All rights reserved.