Do we miscount patent citations? An empirical study on the impact of overlooking the citations to a patent´s pre-grant publication

Utility patent applications are usually published 18 months after they are filed and before patents are actually issued. These so-called pre-grant publications and their corresponding issued patents are both cited individually and concurrently by the applicants or examiners of subsequent patent applications as relevant prior art. Most patent analysts however overlook the citations to the pre-grant publications and consider only those to the issued patents. This study assesses the impact of such omission by comparing the citations to about 140,000 US utility patents and their pre-grant publications. The statistics shows that 70% of the patents are underestimated by various degrees if the citations to their pre-grant publications are ignored, suggesting that analyst should combine the citations to the pre-grant publications and to the patents together when evaluating patents or conducting patent citation analysis.