Title: Spillovers in space
Description: "We simultaneously assess the contributions to productivity of three sources of research and development spillovers: geographic, technology and product-market proximity.  To do this, we construct a new measure of geographic proximity that is based on the distribution of a firm's inventor locations rather than its headquarters, and we report both parametric and semiparametric estimates of our geographic- distance functions.  We find that: i) Geographic space matters even after conditioning on horizontal and technological spillovers; ii) Technological proximity matters; iii) Product-market proximity is less important; iv) Locations of researchers are more important than headquarters but both have explanatory power; and v) Geographic markets are very local"--National Bureau of Economic Research web site.