Conclusions
The recent Þnance literature seems to produce many long-term return
anomalies. Subjected to scrutiny, however, the evidence does not suggest that
market efficiency should be abandoned. Consistent with the market efficiency
hypothesis that the anomalies are chance results, apparent overreaction of stock
prices to information is about as common as underreaction. And post-event
continuation of pre-event abnormal returns is about as frequent as post-event
reversal. Most important, the long-term return anomalies are fragile. They tend
to disappear with reasonable changes in the way they are measured.