New Delhi, Oct. 5 -- The stock market in October is likely to be a below-average performer.

That's not because it's the month in which the two worst crashes in U.S. stock market history occurred. Though that almost certainly is a statistical fluke, it nevertheless has led to endless paranoia about the month.

Instead, according to a new study, the poor odds for this October trace to it being the first month of the calendar quarter. That's when the market typically moves inversely to its performance in the second month of the prior quarter. The S&P 500 index performed very well in August, gaining 2.6% versus a monthly average of 0.7% over the past century.

The study, which recently began circulating in academic circles, is entitled "Corr...