Postmortems of the 2010 Midterm Election Forecasts: Assessing The 2010 State Legislative Election Forecasting Models

Extract

This brief note reports the accuracy of my two forecasts for the 2010 state legislative elections, one made on July 22 and reported in the October 2010 issue of this journal (the “PS model”; Klarner 2010a), and the other made on September 18 and reported in the October issue of Forum: A Journal of Applied Research in Contemporary Politics (i.e., the “Forum model”; Klarner 2010b). Both models used presidential approval, the state of the economy, and midterm loss as national-level predictor variables, while the later forecast also used Gallup's generic ballot question asking respondents which party they would vote for in the upcoming U.S. House election. The PS model predicted the Republicans would pick up 11 chambers, while the Forum model forecast a 15-chamber pickup. In actuality, the Republicans picked up 21 chambers, in contrast to the average 3.2-net chamber shift in party control toward one party or the other from 1962 to 2008. While both forecasts understated the extent of the Republican wave, the July forecast especially did. Overall, the Forum forecast did a good job of predicting the Republican wave, calling about three-fourths of its magnitude.