Knowledge Spillovers and Patent Citations: Evidence from a Survey of Inventors

Abstract

It is well understood that the non-rival nature of as a productive asset creates the possibility of knowledge spillovers, whereby investments in creation by one party produce external benefits by facilitating innovation by other parties. At least since Zvi Griliches's (1979) seminal on measuring the contributions of R&D to economic growth, economists have been attempting to quantify the extent and impact of spillovers. One line of research of this type has utilized patent citations to identify a paper trail that may be associated with flows between firms.' Very little of this research has attempted to determine the modes or mechanisms of communication that actually permit to flow. Further, most of the work has simply assumed that citations or other proxies are sufficiently correlated with flows to allow statistical analysis of the proxies to be informative regarding the underlying phenomenon of interest. This reports on a preliminary attempt to improve this situation. The idea for this survey came from R&D managers whom we were interviewing to test whether the picture of flows produced by patent citations was consistent with the managers' impressions. One of these managers commented that he could not let us talk to the scientists who worked for him, but that he could not stop uls from contacting them via the postal address that appears on their issued patents. The survey results suggest that communication between inventors is reasonably irnportant, and that patent citations do provide an indication of communication, albeit one that also carries a fair amount of noise.