My confidence level on holding the Senate is beginning to get just a little wobbly, so I am pleased to see Sam Wang explain his model. I have a lot of confidence in his abilities to predict election outcomes. I also have a lot of confidence in Nate Silver. The difference between their models is in how they treat so-called “fundamentals,” which are non-polling factors like the historic behavior of a state, the prior political experience of candidates, the state of the economy, as well polling factors unrelated to a specific race, like right track/wrong track, Congressional ballot preference, and presidential job approval.
When you factor in these tangential metrics, it causes election estimates to move more favorably in the Republicans’ direction. Sam Wang estimates that it is giving the GOP a two point bump in Silver’s model, which is enough to flip his prediction of control from blue to red. Wang doesn’t use fundamentals because he thinks they are too unpredictable to be helpful.
I have already written about the real skewed polls. This is an affect of the likely voter screens that pollsters use to try to make their polls more accurate. In 2012, all the likely voter screens were too optimistic, and the most accurate poll was a Ipsos/Reuters poll of registered voters. There are different ways to construct likely voter screens. You can ask respondents how likely they are to vote, how enthusiastic they are, or you can model which responses you use to mirror the expected demographic makeup of the electorate. If you screw this up, as every polling outfit did in 2012, then you miss the mark. Miss your mark badly enough and you’ll make the wrong call, as Gallup did in predicting that Romney would win the popular vote.
In an election in which even Wang predicts the most likely outcome as a 50-50 split, the more assumptions you make, the worse you’re likely to do. This is because the more factors you have, the more likely you are to miss badly on one of them.
And, in this election, nearly all of these extra factors work in the same direction, to improve the Republicans’ chances in the models. Yet, the actual poll numbers despite the likely voter screens have persistently showed the Democrats over-performing expectations.
So, my confidence level has gone down somewhat over the last several weeks, and I think we’re in toss-up territory at this point. When I get the chance, I will sit down and go over the field of play, race by race. In the meantime, Professor Wang is keeping me sane.