Luís A. Nunes Amaral

co-Director, Northwestern Institute on Complex Systems
Professor of Chemical & Biological Engineering
Professor of Physics & Astronomy (by courtesy)
Professor of Medicine (by courtesy)

Chemical & Biological Engineering
2145 Sheridan Road (Room E136)
EvanstonIL 60208US
Phone: (847) 491-7850


We address the question of the growth of firm size. To this end, we analyze the Compustat data base comprising all publicly-traded United States manufacturing firms within the years 1974-1993. We find that the distribution of firm sizes remains stable for the 20 years we study, i.e., the mean value and standard deviation remain approximately constant. We study the distribution of sizes of the ''new'' companies in each year and find it to be well approximated by a log-normal. We find (i) the distribution of the logarithm of the growth rates, for a fixed growth period of one year, and for companies with approximately the same size S, displays an exponential form, and (ii) the fluctuations in the growth rates - measured by the width of this distribution sigma(1) - scale as a power law with S, sigma(1) similar to S-beta. We find that the exponent beta takes the same value, within the error bars, for several measures of the size of a company. In particular, we obtain: beta = 0.20 +/- 0.03 for sales, beta = 0.18 +/- 0.03 for number of employees, beta = 0.18 +/- 0.03 for assets, beta = 0.18 +/- 0.03 for cost of goods sold, and beta = 0.20 +/- 0.03 for property, plant, and equipment.