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Abstract
Estimated rates of return to research are distorted by problems of attributing the credit for particular research results, or for
particular research-induced productivity increases, among research expenditures undertaken at different times, in different
places, and by different agencies. A comprehensive assessment of the evidence from past economic evaluations of the returns
to agricultural R&D indicates that studies generally report high rates of return, with enormous variation among studies, but
that much of this evidence has been tainted by inadequate attention to attribution problems. This paper raises these concerns
in a general way and illustrates their importance with reference to two particular types of attribution problem. First, we
consider the problem of accounting for locational spillovers in attributing varietal-improvement technology among research
performers, using US wheat 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
gains to research expenditures made at different times. © 2001 Elsevier Science B.V. All rights reserved.