Slate's mathematician on the odds the Democrats will flip the House.

A mathematician's guide to the news.
Sept. 19 2006 1:17 PM

Will the Democrats Flip the House?

Slate's mathematician on the odds of a Democratic victory.

(Continued from Page 1)

But remember that Republican strategists told the Washington Post that the Dems have as much as a 90 percent chance of taking the House. Fifty percent isn't close to 90 percent. Why all the predictions of triumph for the Democrats if the party's still running behind?

One explanation is that the tossup races might really be leaning Democratic. Polling in House races is pretty erratic and pretty bad. The data we do have doesn't show a clear swing toward Democrats, but it's possible insiders know something we don't. Pros like Cook and Rothenberg are not just counting seats but evaluating the political climate. Rothenberg believes that national forces will make this a "wave election" like 1994, in which the large majority of tossups and some Republican-leaning seats will turn blue in November.

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There's one more explanation for Dem-friendly projections. Everyone has an incentive to overestimate the chances of a change of hands: A Congress in the balance is a great fund-raising tool for both parties. Plus, for Republicans, selling the impending Democratic victory resets expectations—in the current environment, the Democrats could pick up 14 seats and still come off as losers. Even nonpartisan commentators like Rothenberg and Cook might be inclined to oversell the Democrats. It's more fun to write about a photo finish than a foregone conclusion, and prognosticators get a lot more credit for getting spectacular predictions right than you get blame for getting them wrong.

If you're a Democrat, you've got every right to be hopeful this fall. But if somebody gives you the chance to bet on the GOP, get your wallet out.

Jordan Ellenberg is a professor of mathematics at the University of Wisconsin and the author of How Not to Be Wrong. He blogs at Quomodocumque.

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