Defenders of market efficiency argue that anomalies involving long-term abnormal returns are not robust to alternative methodologies. We argue that because various methodologies use different weighting schemes, the magnitude of abnormal returns should differ, and in a predictable manner. Three problems are identified that cause low power in value-weighted three-factor time series regressions when abnormal returns following managerial actions are being estimated. We illustrate the sensitivities in the context of the new issues puzzle as well as with simulations. More generally, multifactor models as currently used do not, and cannot, test market efficiency.

We study shareholder proposals across a period of substantial activity and find systematic differences both across sponsor identity and across time. To measure the success of shareholder activism, we examine voting outcomes and short-term market reactions conditioned on proposal type and sponsor identity. The voting analysis documents that sponsor identity, issue type, prior performance and time period are important influences on the voting outcome. Proposals sponsored by institutions or coordinated groups appear to act as substitutes gaining substantially more support than proposals sponsored by individuals. The nature of the stock market reaction, while typically small, varies according to the issue and the sponsor identity.