Who will win the Pennsylvania Senate Race?

The US midterms are now just days away with control of the Senate on a knife edge. The race in Pennsylvania has been one of the most hotly contested, with more money spent here by candidates ($133m) than any other.

What makes this race especially fascinating is the huge degree of disagreement between various poll-based forecasts and the betting markets. Here is the percentage chance of each side winning from three different sources:

Win probabilities on 31st Oct 2022

Democratic candidate John Fetterman was favourite in the betting for the entire summer and Republican Mehmet Oz didn't take over at the top of the market until 19 October.

One of the key issues here is Fetterman's health. He suffered a stroke back in May, from which he is still recovering. In the run-up to the one and only TV debate between the two, the betting markets seemed to anticipate that this would likely be a difficult occasion for Fetterman and most observers seemed to agree that he struggled, understandably. This is a pretty good example of how the markets can anticipate the impact of future developments in a way that polling models can't - Fetterman had led in almost every single poll up until the debate, Oz took the lead in those surveys done after.

In some ways Pennsylvania isn't unique here - In other key states like Nevada, Arizona and Georgia the odds generally give the Republicans a better chance than the polling models. There does appear to be a fairly widespread expectation that the GOP will outperfom the polls across the board. No doubt this is a result of Trump's better than expected result in 2020, along with the Republicans performance in a number of Senate races that year. Although Nate Silver explained recently that the main version of the 538 forecast already accounted for a likely better result for the GOP than the raw polling averages might suggest.

Personally, I haven't had a bet in this one, although I might be looking to back Fetterman to win if I think his price gets too inflated by polling doubters nearer the day.