Productivity spillovers in two overlapping networks

This paper studies productivity spillovers from colleagues and co-authors simultaneously in computer science accounting for both quantity and quality of peers. For the identification of colleague spillovers, we model colleagues’ mobility behaviours and use the estimated staying colleagues to instrument for the actual colleagues. For the identification of co-author spillovers, we exploit the characteristics of (estimated staying) colleagues of a scientist’s non-colleague co-authors to construct instruments. Our results provide strong evidence that co-authors generate significant spillover effects, while colleagues generally do not. One additional co-author on average increases a scientist’s productivity by 2%. Further analyses suggest that co-author spillovers function through the sharing of ideas and knowledge, and researchers with more co-authors are more interdisciplinary.