Score contribution per author:
α: calibrated so average coauthorship-adjusted count equals average raw count
Firm numbers first rise, then later fall, as an industry evolves. This nonmonotonicity is explained using a competitive model in which innovation opportunities fuel entry and relative failure to innovate prompts exit; equilibrium time paths for price and quantity also share features of the data. The model is estimated using data from the U.S. automobile tire industry, a particularly dramatic example of the nonmonotonicity in firm numbers. Copyright 1994 by University of Chicago Press.