As loyal readers of this blog are no doubt aware, my forecast of the midterm election was pretty wide of the mark. We don't know the exact number of House seats the Republicans have gained yet, but it looks to be around 65 seats. (I've updated the scatterplot above using this figure.) I had predicted 40 seats, with a 28-seat margin of error. So, while 65 seats is within that margin, it's really out in the tails. And as the scatterplot above shows, it's a huge outlier. I am gratified somewhat that most other forecasters missed it by a lot, too, but the question remains: why did we miss this?
John Sides offers a bit of speculation. One thing he touches on is the importance of candidate recruitment -- the favorable political conditions for Republicans made it easier to recruit high-quality candidates this year. Contrast this with 1994. Yes, Republicans recruited heavily that year, as it was clear that conditions were running against the Democrats, but few believed that the GOP would really take the House that year until right before it happened. Democrats had held the House for forty years; a Democratic House was believed to a permanent part of the political environment. Today, we know that the House can flip back and forth. It was clear by mid-2009 that the economy wouldn't be expanding robustly any time soon, that unemployment was going to remain high, and that Obama's popularity wasn't likely to surge. Add to that the knowledge that a decent set of GOP candidates could actually flip the House, plus a nascent Tea Party movement that was producing potential candidates, and you have a great recruiting environment.
I'm not saying that's the only reason the GOP won so many seats, but it might contribute to it. I'm still wondering about other reasons. I can't help noticing, for example, that the four biggest outliers in the above scatterplot are from the last five midterm elections. Perhaps large swings are a feature of stronger partisanship, or nationalized elections, or something else. But the swings are getting larger.
Meanwhile, a spot of good news for my forecasts: I predicted that Republicans would take over 16 legislative chambers. It looks like they've taken 18, although there are still a few that are up in the air (including the Colorado House).