This study represents the first empirical examination of the "Rule of Three," a theory at odds with several popular notions regarding industry structure and business performance, including the positive linear market share-performance relationship. In general, the findings from more than 160 industries support the Rule of Three and provide five main insights: First, there appears to be a prevalent competitive structure for mature industries in which three "generalist" firms control the market. Second, industries that conform to this structure tend to perform better than industries with a fewer or greater number of generalists. Third, both "specialists" and generalists outperform firms that are "stuck in the middle." Fourth, the performance benefits of market leadership appear to diminish with excessive market share. Fifth, the Rule of Three industry structure and its influence over firm profitability do not appear to be priced appropriately by financial markets. The authors discuss the implications for multiple stakeholders.
Uslay, Can, Z. Ayca Altintig, and Robert D. Winsor. "An empirical examination of the “rule of three”: strategy implications for top management, marketers, and investors." Journal of Marketing 74.2 (2010): 20-39.
American Marketing Association