Event Studies and the Law: Part I: Technique and Corporate Litigation

Event studies are among the most successful uses of econometricsin policy analysis. By providing an anchor for measuring theimpact of events on investor wealth, the methodology offersa fruitful means for evaluating the welfare implications ofprivate and government actions. This article is the first ina set of two that review the use and impact of the event studymethodology in the legal domain. This article begins by brieflyreviewing the event study methodology and its strengths andlimitations for policy analysis. It then reviews in detail howevent studies have been used to evaluate the wealth effectsof corporate litigation: defendants experience economicallymeaningful and statistically significant wealth losses uponthe filing of the suit, whereas plaintiff firms experience nosignificant wealth effects upon filing a lawsuit. Also, thereis a significant wealth increase for defendant firms when theysettle a suit with another firm, in contrast to other typesof plaintiffs, and in contrast to the settling plaintiff firms.These findings suggest that, at a minimum, lawsuits are nota value-enhancing way for corporations to settle their disagreementswith other corporations. In addition, the market appears toimpose a higher sanction on firms than actual criminal sanctions,and reputational losses are of equal magnitude for civil finesas for criminal ones. The article concludes with some recommendationsfor researchers: the standards for conducting an event studyare well established; researchers can increase the power ofan event study by increasing the sample size, and by narrowingthe public announcement period to as short a time frame as possible.The companion article reviews the use of event studies in corporatelaw and regulation.