Geographically localized knowledge: Spillovers or markets?

Using detailed data on California biotechnology, we find that the positive impact of research universities on nearby firms relates to identifiable market exchange between particular university star scientists and firms and not to generalized knowledge spillovers. Poisson and two-stage Heckman regressions indicate the number of star-firm collaborations powerfully predicts success: for an average firm, five articles coauthored by academic stars and the firm's scientists imply about five more products in development, 3.5 more products on the market, and 860 more employees. Stars collaborating with or employed by firms, or who patent, have significantly higher citation rates than pure academic stars.