Solving the halloween indictor puzzle : market efficiency still reigns

Prior research by Bouman and Jacobsen (2002) document unusually high monthly returns over the period November-April for both United States (U.S.) and foreign stock markets and label this phenomenon the Halloween effect. The implication is that the Halloween effect represents an exploitable anomaly, which has negative implications for stock market efficiency. We extend this research to the S&P 500 futures contract and find no evidence of an exploitable Halloween effect over the period April 1982 through April 2003. Re-examining Bouman and Jacobsen’s empirical results for the U.S., we find that two outliers drive their results. These two outliers are associated with the “Crash” in October 1987 and collapse of the hedge fund Long-Term Capital Management in August 1998. After inserting a dummy variable to account for the impact of the two identified outliers, the Halloween effect disappears.