The Election is Looking Good for Both Democrats and Republicans

The election's tomorrow, and if we're to believe the polls and prediction markets, Democrats should recapture the House, while the Republicans should hold on to the Senate. FiveThirtyEight's model, which is based largely on polling but includes other factors that tend to influence midterm elections (e.g., which party controls the White House, fundraising, strength of the economy, etc.), places the probability that Democrats win control of the House at around 88% and that the Republicans maintain control of the Senate at around 81%. Prediction markets are a little less sanguine on the Democrats chances. They only give Democrats a 70% chance of winning the House and a 11% chance of  winning the Senate.

Probabilities are just that, however. An 80% chance that something will happen means that given the current conditions (related to whatever event you're considering), 80% of the time the event will occur, but it also means that 20% of the time it won't.

An intriguing question, though, is how this time around pollsters have handled "outliers." Outliers are survey responses that lie outside of the population trend. They can result from chance or measurement error, and they can throw statistical analyses out of kilter. Pick up almost any academic article that employs a form of statistical analysis (e.g., multivariate regression), and there's a strong chance it'll include "robustness" checks that test or control for outliers.

The key, of course, is whether a perceived outlier is actually an outlier or whether it reflects ground truth. Given what happened in 2016, it wouldn't surprise me in the least to learn that pollsters have been a little conservative when encountering results that appear to favor Democrats. That is, because 2016 polls seemed to have underestimated support for Donald Trump, I can imagine pollsters  dropping any "outliers" that seem to overestimate support for Democrats. If this has indeed occurred (and to be clear I have no evidence that it has), it could mean that Democrats might do better in their quest for seats in both House and the Senate than predicted by current models. That would indeed be a surprise. Almost as surprising as the 2016 presidential election (but not quite).