The economics literature clearly shows that the transmission of knowledge diminishes with physical distance, a factor contributing to industrial clustering. This paper investigates how those distances have stretched over time. We measure the physical distance between collaborating inventors, as...

Using patent citation data for the U.S., we test whether knowledge spillovers in biotechnology are sensitive to distance. Controlling for self-citation by inventor, assignee and examiner, cohort-based regression analysis shows that spillovers are local but that distance is becoming less...