The Meaning of Patent Citations: Report on the NBER/Case-Western Reserve Survey of Patentees

A survey of recent patentees was conducted to elicit their perceptions regarding the importance of their inventions, the extent of their communication with other inventors, and the relationship of both importance and communication to observed patent citations. A cohort of 1993 patentees were asked specifically about 2 patents that they had cited, and a third "placebo" patent that was similar but which they did not cite. One of the two cited inventors was also surveyed. We find that inventors report significant communication, at least some of which is in forms that suggests spillovers from the cited inventor to the citing inventor. The perception of such communication was substantively and statistically significantly greater for the cited patents than for the placebos. There is, however, a large amount of noise in citations data; it appears that something like one-half of all citations do not correspond to any perceived communication, or even necessarily to a perceptible technological relationship between the inventions. We also find a significant correlation between the number of citations a patent received and its importance (both economic and technological) as perceived by the inventor.