21 Nov 2008Working Paper Summaries

Applicant and Examiner Citations in U.S. Patents: An Overview and Analysis

by Juan Alcacer

The ready availability of patent citation data has been a tremendous boon to applied research on knowledge and innovation. The role of examiners in the generation of patent citations has been thought to potentially complicate these analyses, but has been difficult to study. Taking advantage of a change in the way patent citation data has been reported starting in 2001, this paper summarizes basic facts on examiner citations, and provides a descriptive analysis of factors associated with citations in a patent. Key concepts include:

Patent citations reflect the complicated interaction of applicant and examiner strategies, capabilities, and incentives.
Examiner shares are highest in fields where intellectual property tends to be fragmented (computers and communications, for example), and lowest in fields where patents have been shown to be more important in appropriating returns to research and development (such as biomedical and chemical patents).
The most prolific patentees tend to have very high shares of examiner citations.
Examiner citation shares are especially high for foreign firms.

Author Abstract

Researchers studying innovation increasingly use indicators based on patent citations. However, it is well known that not all citations originate from applicants—patent examiners contribute to citations listed in issued patents—and that this could complicate interpretation of findings in this literature. In 2001 the US Patent and Trademark Office (USPTO) began reporting examiner and applicant citations separately. In this paper, we analyze the prior art citations of all patents granted by the USPTO in 2001-2003. We show that examiner citations account for 63 per cent of all citations on the average patent, and that 40 per cent of patents have all citations added by examiners. We use multivariate regression and analysis of variance to identify the determinants of examiner shares. Examiner shares are highest for non-US applicants and in electronics, communications, and computer-related fields. However, most of the variation is explained by firm-specific variables, with the largest patent applicants having high examiner shares. Moreover, a large number of firms are granted patents that contain no applicant prior art. Taken together, our findings suggest that heterogeneity in firm-level patenting practices, in particular by high-volume applicants, has a strong influence on the data. This suggests that analysis of firm-level differences in patenting strategies is an important topic for future research.