Cognitive Distances in Prior Art Search by the Triadic Patent Offices: Empirical evidence from international search reports

Despite large numbers of empirical studies being conducted on examiner patent citations, few have scrutinized the cognitive limitations of officials at patent offices in searching for prior art to add patent citations during patent prosecution. This research takes advantage of the longitudinal gap between international search reports (ISRs) required by the Patent Cooperation Treaty (PCT) and subsequent examination procedures in national phases. It inspects whether several kinds of distances actually affect the probability that a piece of prior art is caught at the time of ISRs, which is much earlier than national phase examinations. Based on triadic PCT applications for all of the triadic patent offices (European Patent Office (EPO), United States Patent and Trademark Office (USPTO), and Japan Patent Office (JPO)) between 2002 and 2005 and their citations made by the triadic offices, evidence shows that geographical distances negatively affect the probability of prior patents being caught in ISRs, while a lag of prior art positively affects the probability. Also, the technological complexity of an application negatively affects the probability, whereas the size of forward citations of prior art affects it positively. These results show the existence of cognitive restrictions borne by officials at the patent offices, and suggest issues for designing work sharing by patent offices, in that the duplication of search costs exists only where search horizons of patent offices overlap each other.