The geography of knowledge spillovers: the role of inventors’ mobility across firms and in space

In this paper we revisit both the JTH test of the localization of knowledge spillovers (Jaffe et al. 1993) and its extension by Agrawal et al. (2006). We find that inventors who patent across different companies and geographical locations contribute extensively to the observed citation patterns, both directly (through personal self-citations) and indirectly, by linking the various companies via a social network conducive to more citations. We also find that social networks convey knowledge both to the mobile inventors’ current locations, and to the prior ones. We conclude that spatial distance is just a proxy for social distance, of which the professional ties between inventors are an important component.