At FiveThirtyEight, we generally prefer state polls to national polls. So far, though, we haven’t had much of them to work with. If you’re getting dozens of national polls every week, but just a smattering of state-level surveys — and that’s what we’ve been getting — you’re better off inferring what’s going on in the states from the trend in national polls, rather than the other way around.
For example, Hillary Clinton has gone from having roughly a 3 or 4-percentage-point lead over Donald Trump in national polls in early July to more like an 8-point lead now. Therefore, we’d expect her to gain perhaps 4 or 5 points in polls of Pennsylvania, Florida, Ohio and other swing states if polls were taken in those states now, compared to the previous versions of those polls conducted a month ago.
On Tuesday, we finally got a bunch of state polls to test the theory — three polls each from Quinnipiac University and Marist College. And, in fact, the new data mostly confirms our hypothesis, although with some caveats. Clinton gained an average of 4 percentage points across the six surveys. The clearest trend toward Clinton is in Pennsylvania, which is now part of her path of least resistance to 270 electoral votes. Here are the new surveys:
Note that these numbers are based on the versions of the polls with third-party candidates included, which is the version FiveThirtyEight’s models use. The head-to-head versions of the Marist and Quinnipiac polls were a bit better for Clinton, perhaps because there are still a fair number of Bernie Sanders supporters who say they’ll vote for Libertarian Gary …