Post-Earnings Announcement Drift

$$PEAD = \frac{SUE}{(\sqrt{var(SUE)}} * \frac{1}{N} \sum^N_{i=1} AR_i$$

where SUE is the standardized unexpected earnings, Var(SUE) is the variance of SUE, N is the number of firms in the sample, and AR_i is the abnormal return of firm i.