Elections can be a little cruel to bank stocks.

Things generally start well, according to a Keefe, Bruyette & Woods (KBW) study of banking and other stocks in the last seven election years.

The Nasdaq Bank Index outperformed the S&P 500 from Jan. 1 to Election Day in every election year since Reagan vs. Mondale. That relationship held true even in the 2008 meltdown year, when the bank index fell 13% and the S&P plummeted 31.5% in the run-up to the Obama vs. McCain vote.

The gap tends to narrow in the four weeks before Election Day, and then things can get dicier for banks between the closing of the polls and yearend, says the study issued Monday.

The bank index underperformed the S&P after the big vote in three of the seven election years — including the last two. For example, in 2004, the S&P rose 7.2% from Election Day to yearend after increasing just 1.7% in the earlier portion of the year. The bank index started off at 5.9% that year then cooled to 4.8% growth after George W. Bush beat John Kerry.

Financial stocks overall, including insurance and other companies, outperformed the marketing going into three of the last four elections, (2004, 2000 and 1996). Financial stocks "lost their steam" and underperformed the market after three of the last four election days.

(These comparisons did not go back further because of the lack of proper data before 1995, the study says.)

Bank stocks this year fit the pattern in the study — so far. The Nasdaq Bank Index had risen 17.6% through Friday, compared with 16.1% for the S&P. Large-cap banks were up 27.5%, and small-to-midsize banks had increased 17.6%.

KBW did not speculate on the causes of the market swings. It also steered clear of any predictions, sticking to the facts at the end: "Election Day is rapidly nearing and will occur on Tuesday, Nov. 6."

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