Postmortems of the 2010 Midterm Election Forecasts: Forecasting House Seats from Generic Congressional Polls: A Post-Mortem

Based on information available in July, we predicted that the Republicans would receive 52.9% of the total House vote and end up holding 229 seats, gaining control from the Democrats in the process (Bafumi, Erikson, and Wlezien 2010b). Our national vote forecast proved to be nearly correct, undershooting the actual Republican share (53.8%) by slightly less than one percentage point. Our seat forecast was a little less accurate. Although we did foresee the House changing hands, we did not predict such a large Republican windfall in seats—we forecast a “mere” swing of 50 seats, which was short of the actual outcome by about 13 seats. The Republican seat total of 242, however, was well within the 95% confidence interval (199 to 259).