This paper demonstrates that the evidence supporting the hypothesis that post-earnings announcement drift (PEAD) is caused by investors’ failure to incorporate the implications of current earnings for future earnings is (also) consistent with researchers’ over-differencing an already stationary time-series. Specifically, we show the evidence is driven by a subset of firms where over-differencing of quarterly earnings in estimating earnings surprises is most likely to have occurred. Given the persistence of the PEAD over time, our alternative explanation suggests that the prior research investigating the causes for the PEAD overestimates investors’ naivete.

In this study of sell-side analysts’ forecasts, we explore the effects of analyst aptitude, learning-by-doing, and the internal environment of the brokerage house on forecast accuracy. Our results indicate that analysts’ aptitude and brokerage house characteristics are associated with forecast accuracy, while learning-by-doing is only associated with forecast accuracy when we do not control for analysts’ company-specific aptitude in forecasting. It is unlikely that this result is caused by measurement errors because it is robust when we use a sub-sample where we can accurately measure experience.