Technological and geographical proximity effects on knowledge spillovers: evidence from the US patent citations

The purpose of this paper is to investigate the pattern of knowledge flows as indicated by the patent citations in three areas: USA, Japan and Europe. In each economic area, we use information from United States Patent and Trademarks Office data to assess empirically the impact of the technological and geographical proximities for 530 international firms. In particular, the contribution to the existing literature is twofold: first, we use an international sample in such a way that we may compare the empirical results among different economic markets; second, we extend the analysis of the determinants of knowledge spillovers, taking into account the time dimension of the effects of the proximities. In order to compute the technological proximity, we follow the methodology developed by A.B. Jaffe (1986. Technological opportunity and spillovers of R&D: Evidence from firms' patents, profits and market value. American Economic Review 76, no. 5: 984-1001), where a technological vector is based on the distribution of patents of each firm across technology classes. As far as the geographic proximity is concerned, we use the latitude and the longitude coordinates of the city in which each firm is situated to obtain the distance, in miles, between the firms. The empirical results, in line with results from previous studies, indicate that there is a statistically significant relationship between the knowledge flows, proxied by the patent citations, and the proximities, but the effects are rather differentiated according to the proximity type.