Growing firms are generally a constant share of the economy with a minor business cycle effect; firms with employment growth outnumber firms with employment decline, and fast growing firms in a given year tend to revert to the mean in later years.
by Brian Headd, U.S. Small Business Administration, Office of Advocacy and Bruce Kirchhoff, New Jersey Institute of Technology
Full Report: http://www.sba.gov/advo/research/rs311tot.pdf