Identifying the age profile of patent citations: new estimates of knowledge diffusion

Abstract

Previous research studies the age profile of patent citations to learn about knowledge flows over time. However, identification is problematic because of the collinearity between application year, citation year, and patent age. We show empirically that a patent's ‘citation clock’ does not start until it issues, and propose a highly flexible identification strategy that uses the lag between application and grant as a source of exogenous variation. We examine the potential bias if our assumptions are incorrect, and discuss extensions into other research areas. Finally, we use our method to re-examine prior results on citation age profiles of patents from different technological fields and application year cohorts. Copyright (C) 2009 John Wiley & Sons, Ltd.

Patent Pools, Competition, and Innovation—Evidence from 20 US Industries under the New Deal

“…Citation-weighted patents increase for both pool and cross-reference subclasses over time, because more recent patents are more likely to be cited Mehta et al 2010). 30 This increase, however, is substantially smaller for pool subclasses.…”

Patent Trolls and Technology Diffusion

“…It is clear that these two patents did not receive enough citations to make analysis precise. Further, the number of citations is small enough that it is difficult to disentangle the decrease in patent citations from the natural decrease in citations observed by Mehta et al (2010). 7 There were no patent licensing lawsuits in this period for this category of software application I could find in searchable court dockets.…”

The impact of convergence between science and technology on innovation

“…The negative binomial model can be used even when an over-dispersion problem occurs because, unlike the Poisson model, it accounts for a bias due to omitted variables and estimates for unobserved heterogeneity. While it is known that most forward citations are received within the first five years after a patent is granted (Mehta et al 2010), some patents may have influenced others even after that time span due to a slower pace of technological development or a change of technological trends. Therefore, the forward citation received might have been calculated as zero value excessively, as we do not consider citations received after five years.…”

“…The higher the number of forward citation received, the more follow-up innovation has been influenced by the concepts and ideas of the focal patent. Since patented technology loses most of its value within the first few years after publication, we only considered forward citations received until five years after the patent was granted to measure innovation impact Mehta et al 2010). …”