Measuring the Returns to R&D: The Depreciation Problem

Measuring the private returns to R&D requires knowledge of its private depreciation or obsolescence rate, which is inherently variable and responds to competitive pressure. Nevertheless, most of the previous literature has used a constant depreciation rate to construct R&D capital stocks and measure the returns to R&D, a rate usually equal to 15 per cent. In this paper I review the implications of this assumption for the measurement of returns using two different methodologies: one based on the production function and another that uses firm market value to infer returns. Under the assumption that firms choose their R&D investment optimally, that is, marginal expected benefit equals marginal cost, I show that both estimates of returns can be inverted to derive an implied depreciation rate for R&D capital. I then test these ideas on a large unbalanced panel of U.S. manufacturing firms for the years 1974 to 2003. The two methods do not agree, in that the production function approach suggests depreciation rates near zero (or even appreciation) whereas the market value approach implies depreciation rates ranging from 20 to 40 per cent, depending on the period. The concluding section discusses the possible reasons for this funding. 1 University of California at Berkeley, University of Maastricht, NBER, and IFS London. email: [email protected]. This is a revision of a paper presented at the International Conference in memory of Zvi Griliches, Paris, August 2003 and the Conference in memory of Tor Jakob Klette, Oslo, Norway, in August 2004. The paper has benefited from comments by participants in those conferences and especially from comments by three referees and the editors of this special issue. The current version contains typesetting corrections as of July 2009. B. H. Hall/Annales August 2007 2 Measuring the Returns to R&D: The Depreciation Problem