Lens or Prism? Patent Citations as a Measure of Knowledge Flows from Public Research

51 Pages Posted: 18 Aug 2012 Last revised: 27 Oct 2014

See all articles by Michael Roach

Michael Roach

Cornell University

Wesley M. Cohen

Duke University - Fuqua School of Business; Duke University - Department of Economics; National Bureau of Economic Research (NBER); Duke Innovation & Entrepreneurship Initiative

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Date Written: August 2012


This paper assesses the validity and accuracy of firms' backward patent citations as a measure of knowledge flows from public research by employing a newly constructed dataset that matches patents to survey data at the level of the R&D lab. Using survey-based measures of the dimensions of knowledge flows, we identify sources of systematic measurement error associated with backward citations to both patent and nonpatent references. We find that patent citations reflect the codified knowledge flows from public research, but they appear to miss knowledge flows that are more private and contract-based in nature, as well as those used in firm basic research. We also find that firms' patenting and citing strategies affect patent citations, making citations less indicative of knowledge flows. In addition, an illustrative analysis examining the magnitude and direction of measurement error bias suggests that measuring knowledge flows with patent citations can lead to substantial underestimation of the effect of public research on firms' innovative performance. Throughout our analyses we find that nonpatent references (e.g., journals, conferences, etc.), not the more commonly used patent references, are a better measure of knowledge originating from public research.

Suggested Citation

Roach, Michael and Cohen, Wesley M., Lens or Prism? Patent Citations as a Measure of Knowledge Flows from Public Research (August 2012). NBER Working Paper No. w18292. Available at SSRN: https://ssrn.com/abstract=2131604

Michael Roach (Contact Author)

Cornell University ( email )

Dyson School of Applied Economics and Management
SC Johnson College of Business
Ithaca, NY
United States

Wesley M. Cohen

Duke University - Fuqua School of Business ( email )

Box 90120
Durham, NC 27708-0120
United States
919-660-4072 (Phone)
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Duke University - Department of Economics

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National Bureau of Economic Research (NBER)

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Duke Innovation & Entrepreneurship Initiative ( email )

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