Applicant and examiner citations in US patents: An overview and analysis

Prior art patent citations have become a popular measure of patent quality and knowledge flow between firms. Interpreting these measurements is complicated, in some cases, because prior art citations are added by patent examiners as well as by patent applicants. The U.S. Patent and Trademark Office (USPTO) adopted new reporting procedures in 2001, making it possible to measure examiner and applicant citations separately for the first time. We analyzed prior art citations listed in all U.S. patents granted in 2001-2003, and found that examiners played a significant role in identifying prior art, adding 63% of citations on the average patent, and all citations on 40% of patents granted. An analysis of variance found that firm-specific variables explain most of the variation in examiner-citation shares. Using multivariate regression, we found that foreign applicants to the USPTO had the highest proportion of citations added by examiners. High-volume patent applicants had a greater proportion of examiner citations, and a substantial number of firms won patents without listing a single applicant citation. In terms of technology, we found higher examiner shares among patents in electronics, communications, and computer-related fields. Taken together, our findings suggest that firm-level patenting practices, particularly among high-volume applicants, have a strong influence on citation data and merit additional research. (C) 2009 Elsevier B.V. All rights reserved.