Should you dump all your stock market funds on the first of May, go away, and come back again for Halloween? Definitely, says an old Wall Street adage. Definitely not, say most financial advisers.

As for the evidence of history? It’s more ambiguous. If the numbers say anything, maybe it is that “sell in May and go away” is only half-right. Since 1900, someone who sold in May actually could have retired earlier and with more money — but only if they hung around and waited to buy their stocks back during the usual summer panic.