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 resulis imply ihat ihe mosf important sources of economic rents are business-specific; industry membership is a much less important source and corporate parentage is quite unimportant.

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Prior work has shown an association between diversification strategy and profitability. This paper replicates that association using more recent and complete data and goes on to investigate the sources of the association. Theoretical arguments are advanced which predict the association which will remain once the effects of varying industry profitability are removed. Empirical tests verify this prediction and permit the discrimination between the effects of industry and diversification strategy on profitability.