Election forecast predicts democrats will gain 3 seats in Senate, 11 in House

October 21, 2008

An election forecast model developed by a political scientist 99 days before the 2008 elections and before the recent Wall Street crisis predicts significant Democratic gains in the 2008 congressional elections—including 11 seats in the U.S. House of Representatives and 3 seats in the U.S. Senate.

The predictions are made in an article authored by Carl Klarner (Indiana State University) and published in an election-specific symposium in the October 2008 issue of PS: Political Science and Politics, a journal of the American Political Science Association (APSA). The full symposium is available online at www.apsanet.org/content_58382.cfm>.

Traditionally, efforts to call elections rely either on district- and state-level analyses limited to recently collected information (such as polls) or aggregate forecasting models measuring national trends. Klarner notes that "most forecasting models of House and Senate elections have not made predictions at the state or district level" and that "how national factors influence election outcomes is contingent on the distribution of votes across districts or states." His 2008 forecast refines his own previous work in this area to use a model that combines both approaches.

The House and Senate forecasts were made in late July 2008, and the author's model focuses on the percent of the major-party vote that the Democratic candidate received in a state or district. Klarner considers three main sets of factors in examining past elections from 1954 onward: district partisan composition, candidate attributes, and national partisan tides. The weighting of these factors is based on a range of historical and empirical data—including most recent votes for Democrats in a district; results of the most recent presidential vote; incumbency; prior experience in candidates; national vote intentions reported in surveys; presidential approval; performance of the economy; and the "midterm penalty" for the president's party.

The model's House prediction includes the following items of note:

-- Democrats will receive 247 seats in the House—a gain of 11 seats overall.
-- There is a 95% probability that Democrats will have between 233 and 266 seats after the election and a 67% probability that they will have between 240 and 255 seats.
-- There is a about a 0% probability that the Democrats will lose control of the House.

The model's Senate prediction includes the following items of note:

-- Democrats will have 54 Senate seats after the election—a net gain of 3.
-- There is a 95% probability that the Democrats will win between 12 and 19 seats out of the 35 seats up this election.
-- There is a 2.4% chance the Democrats will lose control of the Senate.
-- There is a 0.3% chance that the Democrats will obtain a filibuster-proof majority of 60 seats.

By integrating long-term data analysis with current local and national political factors, this election forecast model reflects ongoing efforts by political scientists to analyze election dynamics in the US. Notably, this prediction of the outcome of the 2008 congressional election was made well before the recent Wall Street financial crisis has made the political landscape more favorable to Democrats.

Source: American Political Science Association

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