Why the Whole Trump-Clinton Election Could Probably Just Be Held in Pennsylvania

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SOURCE: NEW YORK TIMES

URL: http://www.nytimes.com/2016/09/17/upshot/why-the-whole-trump-clinton-election-could-probably-just-be-held-in-pennsylvania.html

by: Toni Monkovic


With her polling lead slipping, Hillary Clinton still has Pennsylvania as a firewall — for now.

David Rothschild, an economist at Microsoft Research who runs PredictWise, an online forecasting model that relies on betting markets, explained the primacy of Pennsylvania for Mrs. Clinton’s election chances during an interview this week.

He also discussed the potential importance of the ground game, the perceived failure of betting markets in predicting “Brexit” and the ethics of live forecasting on Election Day, among other topics. Here’s the lightly edited text of our email exchange.

Pennsylvania

Q. Based on the PredictWise state polling probabilities, the entire election could boil down to Pennsylvania. If Hillary Clinton wins the state, she’ll probably be president. If Donald J. Trump wins there, he’ll probably be president — because such a victory would suggest he’d also win Ohio, Florida, North Carolina. Today, PredictWise gives Clinton a 78 percent chance to win the state. This is close to The Upshot forecast (85 percent). Can you give some more insight into what makes Pennsylvania so important and what signs you’ll be looking for in the state in the next few weeks?

A. Pennsylvania has been the most likely tipping-point state since midsummer.

It has been the state to put Hillary Clinton over 270 electoral votes, should she win all of the other more likely states for her. Conversely, it’s also the state that would put Trump over the hump, if he wins all of the states that are more likely for him.

Every day, I run 100,000 simulations of the election. I use the probability of each state going for Clinton or Trump, then I mix that with a correlation matrix that defines the relationships between the states. And every day since late July, Pennsylvania has been the state that most frequently is won by the candidate who wins the election. Currently, there are just 6 percent of scenarios where Clinton wins Pennsylvania but loses the election, and just 3 percent of scenarios where Clinton loses Pennsylvania and wins the election.

Since Pennsylvania is more secure for the Clinton camp than other swing states, it’s unlikely that Clinton loses Pennsylvania and wins either Florida or Ohio or other states to make up for the necessary electoral votes. And Trump could take Florida and Ohio and North Carolina, and go over the top with some other combination of swing states. But Pennsylvania is his most likely route.

What I will be looking for in Pennsylvania over the next few weeks is simple: polls in Pennsylvania; polls in Ohio, which have similar demographics (and a lot of polling); and national polls that correlate heavily among the key swing states.

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