As summer closes in, many advisers will start claiming that the “summer rally” will be coming with it, says MarketWatch’s Mark Hulbert. But, Hulbert says, don’t listen to them.

“The ‘summer rally’ that, like clockwork, [advisers] start referring to around Memorial Day is entirely a figment of their imagination,” Hulbert writes. For each month of the year going back to 1940, he looked at the stock market’s average return from month end to its highest close over the next three months. On average in the three months following May, the market has topped out around 4% higher than where it has been at the end of May. That’s lower than the average of 7 other months.

Hulbert says that in some years, the market “on no occasion in June, July or August was higher than where it was at the end of May.” He adds that “these calculations are based on the market’s highest close during a three-month window, and that level is known only after the fact. Sometimes it occurs early in the three-month window and, at other times, at the end. So while the [data] reflects maximum rally potential, actually realizing that potential would require perfect clairvoyance — what statisticians refer to as hindsight bias.”