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University of Pennsylvania Carey Law School

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Power And Statistical Significance In Securities Fraud Litigation, Jill E. Fisch, Jonah B. Gelbach Jan 2021

Power And Statistical Significance In Securities Fraud Litigation, Jill E. Fisch, Jonah B. Gelbach

All Faculty Scholarship

Event studies, a half-century-old approach to measuring the effect of events on stock prices, are now ubiquitous in securities fraud litigation. In determining whether the event study demonstrates a price effect, expert witnesses typically base their conclusion on whether the results are statistically significant at the 95% confidence level, a threshold that is drawn from the academic literature. As a positive matter, this represents a disconnect with legal standards of proof. As a normative matter, it may reduce enforcement of fraud claims because litigation event studies typically involve quite low statistical power even for large-scale frauds.

This paper, written for …


Docketology, District Courts And Doctrine, David A. Hoffman, Alan J. Izenman, Jeffrey Lidicker Jan 2007

Docketology, District Courts And Doctrine, David A. Hoffman, Alan J. Izenman, Jeffrey Lidicker

All Faculty Scholarship

Empirical legal scholars have traditionally modeled trial court judicial opinion writing by assuming that judges act rationally, seeking to maximize their influence by writing opinions in politically important cases. Support for this hypothesis has reviewed published trial court opinions, finding that civil rights and other "hot" topics are more likely to be explained than purportedly ordinary legal problems involved in resolving social security and commercial law cases. This orthodoxy comforts consumers of legal opinions, because it suggests that they are largely representative of judicial work. To test such views, we collected data from a thousand cases in four different jurisdictions. …