The large observed variance component for business-unit effects overshadows the other variance components. Although this model cannot reveal the sources of this dispersion, some insight can be gained by examining Schmalensee's results on the importance of market share. His study of sample A for 1975 measured a variance component due to share of 2.2. This amounts to 1.7 percent of the business-unit variance component estimated for sample A data in this study. Hence, it seems safe to conclude that only a very small part of the large business-unit effects can be associated with differences in the relative sizes of business-units.