This study partitions the total variance in rate of return among FTC Line of Business reporting units into industry factors (whatever their nature), … - Richard P. Rumelt

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This study partitions the total variance in rate of return among FTC Line of Business reporting units into industry factors (whatever their nature), time factors, factors associated with the corporate parent, and business-specific factors. Whereas Schmalensee (1985) reported that industry factors were the strongest, corporate and market share effects being extremely weak, this study distinguishes between stable and fluctuating effects and reaches markedly different conclusions. The data reveal negligible corporate effects, small stable industry effects, and very large stable business-unit effects. These results imply that the most important sources of economic rents are business-specific; industry membership is a much less important source and corporate parentage is quite unimportant.