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26 Oct, 4 tweets, 2 min read
I would note that the gap is a little bit narrower in our *forecast*: Biden +5.1 in Pennsylvania vs. +7.8 in the national popular vote. projects.fivethirtyeight.com/2020-election-…
Why is Biden +9.1 in our national poll average but +7.8 in our forecast?

* The forecast still assumes just a teensy bit of tightening (about 0.4 points toward Trump)
* The forecast is mostly based on state polls, which have been more consistent with an ~8 point lead than 9-10.
Why this state/national poll gap exists is an interesting question. Also there have been points in the year where it seemed to run in the opposite direction, e.g. before the first debate, our model thought Biden led by ~8 points from state polls vs. a ~7 point national poll lead.
FWIW, the current implementation of our model is sparing with how it uses national polls. You could argue for moving Biden's state polls upward slightly so that they better match the national polls. Our 2012 & 2016 models did that to some degree, but this year's does not really.

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More from @NateSilver538

Nate Silver Profile picture
28 Oct
I'm not sure that some of these early-voting comparisons to 2016 make a ton of sense given that much of Biden's edge is thought to come from independents breaking his way, and early voting statistics won't capture that.
For example, Biden lost independents by 13 points in Nevada in 2016, per the exit poll there. This year, he leads them by 3 points, in an average of the last 6 polls of the state. That amounts to a net 6 point swing to Biden.
In many state/national polls, Biden also gets a slightly higher share of Republicans than Trump does of Democrats. In Nevada polls, for instance, Trump gets 6% of Democrats but Biden gets 9% of Republicans. That's amounts to about a 2 point swing to Biden vs. 2016.
Read 5 tweets
Nate Silver Profile picture
26 Oct
I think there are basically 3 groups of polls that herd.

1) Some (certainly not most or all) online or IVR polls with crappy raw data seem to look to live-caller polls for guidance. They tend to stay pretty close to the averages throughout the year.
2. Some partisan and quasi-partisan pollsters seem to play a lot of games with the 538 and RCP averages. They don't want to stray *too* far from the average, but they'll often show results that are like the 538 or RCP average shifted by 2 points toward their side.
3. Some high-prestige academic and media pollsters may be scared to publish a perceived outlier very late in the race, when they think it could hurt their reputation. For most of the year, these pollsters are the ones you trust NOT to herd. But sometimes their final polls are 🤔.
Read 4 tweets
Nate Silver Profile picture
26 Oct
I don't think it's really worth talking about individual polls from firms that have a poor track record and I wouldn't particularly trust to act in good faith.
And it's really the good faith part that matters. A firm that has a middling track record but I can trust to do honest work ... at least you can get some sense of direction from the poll. Different when the pollster seems to be engaged in a game to manipulate the media narrative.
Usually, manipulating the media narrative is what (some) partisan pollsters do. We include partisan polls in our averages but they're handled differently and weighed less. But there's a gray zone of firms that act like partisans even though they technically aren't by our rules.
Read 5 tweets
Nate Silver Profile picture
24 Oct
Hey folks, our national polling average is now Biden +9.2, as compared with Biden +9.7 yesterday. What caused the change given that the national tracking polls were decent for Biden this AM? It's older polls dropping out of the average.

projects.fivethirtyeight.com/polls/presiden…
Following major events like debates, our average shifts forward the window of time that it considers, and more recent polls have indeed been more consistent with a Biden lead of about 9 points nationally; haven't seen as many of those Biden +14s lately.
It's not perfect, and we'll probably tinker with these mechanics post-2020, but keep in mind that our averages are really a blend of an RCP style average over a fixed window of time (where this sort of thing happens a lot) and a HuffPost/Pollster style trendline.
Read 4 tweets
Nate Silver Profile picture
22 Oct
It's definitely a source of uncertainty and different ways that pollsters are handling early and mail voting vis-a-vis likely voter models probably explains some of the differences we're seeing between polls right now.
I think there's *probably* more upside risk than downside risk for Democrats here (i.e. that turnout will be bluer than likely voter models project) but I can also imagine scenarios where it leads pollsters to underestimate the R vote instead.
For instance, if you had a fixed estimate of turnout (as X% of registered voters) and you put people who had already voted first in the queue, then mostly GOP election day voters might get crowded out. That's a weird way to do a likely voter model but some pollsters might do it.
Read 5 tweets
Nate Silver Profile picture
22 Oct
Based on an update we'll be releasing later today, we're now projecting total turnout in the presidential race to be 154 million, with an 80th percentile range between 144 million and 165 million. In 2016, turnout was 137 million, by comparison.
The primary ingredient in our turnout estimate is polls that ask people whether they're more or less enthusiastic about voting than usual, and those polls are showing record levels of enthusiasm.
We've also increased our estimate based on academic research showing expanded voting options (e.g. no-excuse absentee voting) tends to increase turnout, as well as new @ElectProject estimates of the voting-eligible population, which is higher than what we'd used previously.
Read 5 tweets

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