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>  News Releases >   2006 >   October

New study forecasts Democratic takeover of U.S. House

Dartmouth College Office of Public Affairs • Press Release
Posted 10/30/06 • Genevieve Haas • (603) 646-3661

Statistical analysis predicts 32-seat gain
Joseph Bafumi
Joseph Bafumi (Photo by Joseph Mehling '69)

A new study, "Forecasting House Seats from Generic Congressional Polls" authored by Dartmouth Professor of Government Joseph Bafumi and colleagues at Columbia and Temple universities, predicts that based on current ballot polling data, the Democratic Party can expect to gain 32 seats in the U.S. House of Representatives in the Nov. 7 mid-term congressional elections. Such a gain would guarantee the Democrats a House majority and exceed many current forecasts for Democratic gains in the House.

The study, co-authored by Robert Erikson of Columbia University and Christopher Wlezien of Temple University, translates the results of generic congressional polls conducted by CNN, USA Today/Gallup, ABC/Washington Post, Fox/Opinion Dynamics and Newsweek into the partisan midterm swing. The polling data they used asked respondents which party they would choose in the next election. According to that analysis, Democratic congressional candidates are predicted to receive 55 percent of the votes cast, plus or minus a few percentage points.

The study then goes on to analyze whether that majority of votes is likely to translate into a majority of House seats. Combining the partisan swing, estimated from the generic congressional polls, with historical data at the congressional district level, they predict which party will win each district race. The researchers found that if Democrats receive even 53 percent of votes cast, the probability that they will win enough seats to take over the House increases to more than 90 percent.


If Democrats receive at least 53% of the vote, they have a 90% probability of winning enough seats to control the House. If they win more than 53%, that probability rises to approach 100%.

Although Bafumi and his colleagues are far from the first prognosticators to analyze poll data as a predictor of a party's political fortunes, their analysis differs from that of most pollsters and pundits in its rigorous and non-partisan evaluation of the true statistical value of polling. According to Bafumi, "This sophisticated statistical model suggests that the Democrats should out-perform the expectations of many in 2006."

Download the study. (233kb PDF)

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