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    November 1, 2006
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Political scientists predict Dems gain House based on poll analysis


After reviewing voter polls for the upcoming Nov. 7 congressional elections, a group of political scientists forecast that Democrats should gain 32 seats in the House, making Democratic control of that chamber “a near certainty.”

The prediction is part of detailed analysis of recent polls that examines current trends and compares these responses with those from midterm elections going back to 1946. 

Christopher Wlezien
(Photo by Joseph V. Labolito / University Photography)

Using computer simulation based on statistical analysis of the historical data, the political scientists from Dartmouth College, Columbia and Temple universities say the current patterns show Democrats making big gains.

The three researchers who worked on the analysis are Joseph Bafumi of Dartmouth, Robert S. Erikson of Columbia and Christopher Wlezien of Temple.

“If current trends in the congressional generic ballot polling persist (which they have in past elections), the Democrats are near certain to win control of the House,” the three write in an analysis released last week.

Of course, in the rapid-fire world of election politics, unexpected events could make a change in the predictions. 

One telling factor, say the researchers, is the lead Democrats have over Republicans in these polls. If the Democrats hold on to a lead of at least 8 points among likely voters, a Democratic majority in the House is very likely.

“If the lead dips below this level, the Republicans can rekindle their hope of holding the House,” they write.

Their prediction is based on six polls of likely voters conducted during the past 30 days of the campaign for a period ending Oct. 23.  The polls were two conducted by CNN, and one each from ABC/Washington Post, Fox/Opinion Dynamics, Gallup/USA Today and Newsweek.

Ray Betzner


Figure 1.  Summary of simulated election outcomes predicted from varying generic ballot poll results

The Democrats need more than the plurality of the generic vote in order to expect to control the House.  Above, in the range where the Democrats have between 50 and 52 percent of the “two-party” generic vote, majority control is up for grabs — around .50 probability.  But one percentage point more, and the probability shoots up. If the Democrats have 53 percent or more of the vote by the generic ballot question, as they do as of this writing, they are the heavy favorites (probability > .90) to win the House of Representatives.




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