One of the criticisms of election predictors in 2016 was that some people felt that the risks and potential for errors were not explained. I don’t think Beto will win the Senate but his odds right now are somewhere in the range of rolling a die and getting a 6 or rolling a die and getting either a 5 or 6 which basically says that weird things can happen but they probably won’t. So I am writing this post so that no one can say I misrepresenting Cruz winning Texas as a sure event or was not clear about the possibility of a model/poll error, not because I am trying to hedge my bets.
But there are several factors at play that could cause the polls and my model to be wrong in Texas and other Senate races. I trust my model and the polls, but I know from experience that there are a few cases where the polls and my model have issues predicting a winner, and I wanted to share that those scenarios. I don’t want to give the impression that my model is perfect and always right because it isn’t. No statistical model is ever always right, and something as incredibly complicated as an election means that nothing is ever certain. But I do know my model on average predicts the outcome by 2.5 points in presidential elections and calls the winner over in over 90% of the races. I have never predicted Senate races, but I have no reason to believe this will change significantly. Some people may wonder why I ever bother to predict something that will eventually happen, knowing that I am going to wrong sometimes. But I do this because it’s fun and it makes election night more exciting to have some skin in the game.
Scenario 1: Systemic Polling Error (Beto wins by 2 or more points)
Under this scenario, the polls failed to capture the enthusiasm of young and minority voters and incorrectly estimated who would turnout. There are a lot of telephone polls, and they are probably more apt to miss Beto’s base than internet polls. On great example of this is a New York Times / Sienna College Poll . They struggled to get young, and minority voters and the categories were reweighted, However, when you don’t get an accurate sample, you introduce error. It’s not the pollsters fault for this since they have to randomly sample and they can’t make you answer. I’ve talked about the importance of poll participation before. Sometimes polls are wrong because they aren’t conducted properly but the vast majority of the time its because not the right group of people answered. Under this scenario, Beto would win by at least 2 points because that’s the minimum error you would need to see for the polls to be considered abnormally wrong.
Scenario 2: Republicans Stay Home
In this scenario, Republicans don’t turn out like they did in past elections. The rough indicator of this is the exit poll, but it may not be detailed enough to conclude this happened. Another proxy for this is relative turnout in the strong Republican counties versus the more urban and liberal counties. If turnout is unexpectedly weak among Republicans, this would also hurt the polls as well which were probably designed with Cruz having a turnout advantage.
Scenario 3: The Polls aren’t “Wrong” and Beto still wins by less than a point
This seems like a contradiction, but its normal for Senate polls to be wrong by about 5 points on average. And Cruz has slightly below a five-point lead in the polls. So Beto could win by less than a point, and the polls would still perform like they usually do. Competitive races are really hard to poll and predict because a lot of the time there will be a statistical tie.
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