Compare methods

	Event Study Methodology	Diversification-Performance Analysis (Rumelt Categories)
Field	Strategic Management	Strategic Management
Family	Process / pipeline	Process / pipeline
Year of origin	1997	1974
Originator	A. Craig MacKinlay; Stephen J. Brown & Jerold B. Warner	Richard P. Rumelt; Krishna Palepu
Type	Abnormal-return estimation pipeline for valuing corporate events	Classification-and-comparison pipeline relating diversification type to firm performance
Seminal source	MacKinlay, A. C. (1997). Event Studies in Economics and Finance. Journal of Economic Literature, 35(1), 13-39.	Rumelt, R. P. (1974). Strategy, Structure, and Economic Performance. Division of Research, Graduate School of Business Administration, Harvard University. ISBN: 9780875841090
Aliases	Abnormal Returns Analysis, Cumulative Abnormal Return (CAR) Analysis, Stock-Market Event Study, Market-Model Event Study	Rumelt Diversification Category Analysis, Related vs Unrelated Diversification Analysis, Corporate Diversification Strategy Classification, Diversification Strategy-Performance Linkage
Related	3	3
Summary	Event study methodology measures the stock-market reaction to a discrete corporate event by isolating the portion of a firm's return that cannot be explained by normal market movements. Under semi-strong market efficiency, new information about an acquisition, earnings announcement, alliance, CEO change, or regulatory shock is impounded into prices almost immediately, so the abnormal return around the event date is a clean, forward-looking estimate of the event's value consequences. A. Craig MacKinlay's 1997 survey codified the canonical pipeline -- define the event and windows, estimate a normal-return benchmark, compute abnormal returns, accumulate them into a cumulative abnormal return (CAR), and test significance. Brown and Warner's 1985 study established the statistical properties of these procedures with daily data, showing when simple methods are well specified and how variance and clustering must be handled. The method is the workhorse for linking strategic decisions to shareholder value.	Diversification-performance analysis asks whether the kind of diversification a firm pursues — staying focused, expanding into related businesses, or building an unrelated conglomerate — is systematically associated with how well the firm performs. The categorical version originates with Rumelt's 1974 Strategy, Structure, and Economic Performance, which classified diversified firms by specialization and relatedness ratios into single-business, dominant-business, related, and unrelated types and found that related diversifiers tended to outperform unrelated ones. Palepu's 1985 study reframed diversification with the continuous Jacquemin-Berry entropy measure, again finding that related diversification was associated with superior profit growth, and showed how the index approach and Rumelt's categorical method can be combined to gain both objectivity and conceptual richness.