Historically, September has been the worst-performing month for stocks spanning the last century, on average. It is also the most-frequently down month over the same period. Nevertheless, the effect has been attributed by most economists to chance (one month has to be the worst, after all). Depending on the time period under consideration, the September Effect may be present, or not. Research taking an even longer time horizon back over 300 years (using U.K. data since 1693) shows no evidence at all of the Effect. September mean returns are actually higher than the returns during the other months for 3 out of the 6 50-year subperiods, although the difference is not statistically significant.