Seasonality in Stock Price Mean Reversion: Evidence from the U.S. and the U.K.

The evidence of slowly mean-reverting components in stock prices has been controversial. The hypothesis of stock price mean-reversion is tested using a regression model that yields the highest asymptotic power among a class of regression tests. Although the evidence that the equally weighted index of stocks exhibits mean-reversion is significant in the period 1926–1988, this phenomenon is entirely concentrated in January. In the post-war period both the equally weighted and the value-weighted indices exhibit seasonal mean-reversion in January. A similar phenomenon is also observed for the equally weighted index of stocks traded on the London Stock Exchange.