Patent Citations and Triadic Closures as Private Value Indicators

The number of forward patent citations has been established as an indicator for the economic value of patents. There remain unresolved questions such as the difference between examiner citations and inventor citations as value indicators and whether and how local clustering coefficients of added citations affect the private value of cited patents. These questions are related with the problem of patent thickets since examiner citations reflect them more directly than inventor citations. Also, higher local clustering coefficients imply denser networks (more triadic closures) of patent citations around a patent, suggesting that local clustering coefficients can be a measurement of subsequent growth of patent thickets. In order to explore the relationship between the value of patents and the clustered nature of patented citations, this study employs survival analysis of patent renewals, based on Japanese patent and citation data. Results show that both examiner and inventor citers are correlated with the private value of cited patents, but there are differences. Triadic closure citers made by examiners are statistically significant factors for private value, whereas inventors' triadic closure citers are not. The findings above illuminate the advantage of examiner citations, which are sometimes thought to be "noise" as knowledge spillover proxies.