Stars and Brokers: Knowledge Spillovers Among Medical Scientists

This paper estimates the heterogeneity in peer effects among research scientists in terms of network position. I propose a new measure, brokerage degree, that determines the extent to which a scientist depends on a coauthor to provide him unique access to other scientists further away. I apply this measure to the coauthorship network of medical scientists. I show that network position is crucial for productivity by facilitating access to nonredundant knowledge. Identification results from variation in brokerage degree among coauthors linked to a star scientist who dies. A one standard deviation increase in the brokerage degree of a deceased star is associated with a 10% decrease in annual publications of his coauthor. By applying brokerage degree to topics, I provide evidence that access to knowledge flows embodied in scientists further away can account for a large proportion of the identified heterogeneity effect.