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

The purpose of this paper is to investigate the pattern of knowledge flows as indicated by patent citations. In order to compute the technological proximity, we have followed the methodology developed by Jaffe (1986), 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 have used the latitude and the longitude coordinates of the city in which each firm is located. The empirical results suggest that the effects of proximity variables on knowledge flows are rather differentiated.