This paper shows that short horizon stock returns can be predicted to a much greater degree by past price movements than would be anticipated given their low autocorrelation. This raises doubts over the reliability of the autocorrelation statistic as a measure of stock market predictability.

We investigate whether the use of component forecasts improves the accuracy of a portfolio forecast which uses only aggregate data. The results show that the use of component data improves the accuracy of aggregate forecasts. Furthermore, the long–short trading strategy based on the component...