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What State Polls Can Tell Us About The National Race

Earlier this week, I was working on an article that claimed Joe Biden had better results in state polls than in national polls.

Then on Wednesday, the inevitable happened. Biden had some excellent results in national polls, including 10-point leads in high-quality national polls from Quinnipiac University and Marquette Law School, bringing his margin in our national polling average up to 7.3 percentage points. And he had some pretty bad state polls. ABC News/Washington Post polls showed him narrowly trailing President Trump in Florida and Arizona, for example, two states where he has usually held leads. (All numbers in this article are as of late Wednesday afternoon.)

Still, it’s worth thinking about what state polls can tell us about the national race. Suppose, for instance, that there were no national polls, and instead, we had to guess what the national popular vote would be from state polls. Actually, this wouldn’t be that hard at all!

Since we know how the states vote relative to the nation, we can use state polls to estimate national results. Florida, for instance, is typically about 3 points more Republican than the average state. So if Biden were ahead by 2 points in Florida, it would imply that he was ahead by 5 points nationally.

Why bother with this when we can just look at national polls directly?

Well, one good reason is that if used properly, state polls can actually give you a better projection of the national popular vote than national polls themselves! In 2012, for instance, our model — which then, like now, mostly uses state polls to forecast the national popular vote — showed then-President Barack Obama winning the popular vote by approximately 3 points, even though his lead in national polls was only about 1 point. Indeed, the state polls provided the better estimate of the national popular vote than the national polls did. (Obama won the popular vote that year by around 4 points.)

Keep in mind that there is a lot of information contained in those state polls. They may do a better job of estimating the preferences of demographic groups that are more common in their states — Cuban Americans in Florida, or Mormons in Utah, for example — than national polls ever could. And at least this year, the pollsters conducting state polls tend to be more highly rated than those doing national polls, especially with pollsters like New York Times/Siena College and our colleagues at ABC News1 doing more state polling this year than in the past.

So let me run you through a simplified version of how our model uses those state polls. It’s similar to the example about Florida above. In each state, our model calculates the national margin based on a state’s partisan lean, plus Biden’s current lead or deficit in our polling average. Here is that calculation for a broad group of purple states (or congressional district in the case of Nebraska) — everything on the spectrum from purple-red (maroon?) states like Texas to purple-blue (indigo?) states like New Mexico. I’ll show you the national margin based both on how a state voted in 2016 and how it voted in 2012 — in some cases, there are significant differences.

What purple state polls say about the national race

Biden’s polling lead or deficit in close states, and what that means for his national margin, based on 2016 and 2012 results

Biden national margin
State Biden’s current lead or deficit* Based on 2016 results Based on 2012 results
Texas -0.7 +10.4 +18.9
Georgia -1.0 +6.2 +10.7
Iowa -1.0 +10.5 -3.0
Ohio -1.0 +9.2 -0.1
Arizona +3.8 +9.4 +16.7
Nebraska 2nd District +4.3 +8.6 +15.3
North Carolina +1.2 +6.9 +7.1
Florida +1.7 +5.0 +4.7
Pennsylvania +4.6 +7.4 +3.1
Wisconsin +6.8 +9.7 +3.7
New Hampshire +6.9 +8.6 +5.2
Michigan +7.5 +9.8 +1.9
Minnesota +9.2 +9.8 +5.4
Nevada +5.8 +5.5 +3.0
Virginia +11.3 +8.1 +11.3
Colorado +10.2 +7.4 +8.7
Maine +13.9 +13.0 +2.5
New Mexico +12.9 +6.8 +6.6
Average (weighted by turnout) +3.6 +8.1 +7.2

*Based on FiveThirtyEight polling averages as of 4:10 p.m. Eastern on Sept. 23. States (or district in the case of Nebraska) are included only if they have at least five total polls or polls from at least three pollsters. Sorted from reddest to bluest.

As of late Wednesday afternoon, for example, Biden led by 6.8 percentage points in our polling average in Wisconsin. It’s clearly good news for Biden that he’s leading in Wisconsin, but what it implies about the national race depends on what year you’re comparing it with. In 2016, for instance, Wisconsin was about 2.9 points more Republican than the nation, so having a 6.8-point lead there would imply that Biden had a huge 9.7-point lead nationally. But in 2012, Wisconsin was 3.1 points more Democratic than the country overall, so a 6.8-point lead would imply only a 3.7-point national margin.

Indeed, you can see in the chart where Biden is running especially well or comparatively poorly relative to how the state usually votes. The fact that Biden is nearly tied with Trump in Texas is extremely impressive for Biden, for example. But it’s not a great sign for him that his lead in Florida is so narrow. In states like Iowa, Ohio, Michigan and Maine — which swung strongly against Hillary Clinton in 2016 — Biden’s performance is very impressive relative to four years ago, but not so much as compared with 2012.

However, averaging each state’s implied national margin and weighting it based on each state’s turnout puts Biden ahead by 8.1 points nationally if you’re using 2016 as a baseline, or 7.2 points if you’re using 2012 instead. In this case, that’s pretty similar to his current 7.3-point lead in national polls.

But what about polls in deeply red states and deeply blue states? Those states may not create much Electoral College suspense, but they do count toward the popular vote. First, Biden’s national margin in red states that have a sufficient2 amount of polling:

What red state polls say about the national race

Biden’s polling lead or deficit in traditionally Republican states, and what that means for his national margin, based on 2016 and 2012 results

Biden national margin
State Biden’s current lead or deficit* Based on 2016 results Based on 2012 results
Oklahoma -23.6 +14.9 +13.8
Kentucky -18.6 +13.3 +7.9
Alabama -14.9 +14.9 +11.1
Utah -12.4 +7.6 +39.3
Tennessee -12.3 +15.8 +11.9
Kansas -9.3 +13.2 +16.1
Louisiana -10.7 +11.0 +10.4
Montana -8.0 +14.3 +9.5
Indiana -14.4 +6.7 -0.3
Mississippi -11.7 +8.2 +3.7
Missouri -6.7 +13.9 +6.5
South Carolina -6.8 +9.6 +7.5
Average (weighted by turnout) -12.4 +12.0 +9.8

*Based on FiveThirtyEight polling averages as of 4:10 p.m. Eastern on Sept. 23. States are included only if they have at least five total polls or polls from at least three pollsters. Sorted from reddest to bluest.

Biden’s actually polling comparatively well in many of these red states. He’s not much of a threat to win them, but in a fair number of them, his deficit is in the single digits when Democrats usually lose them by the double digits. Whether this is real or reflects dubious polling is harder to say, however.

In very blue and very red states, it’s not uncommon for polls to underestimate the winning candidate’s margin. But maybe Biden, who isn’t as easily typecast as a liberal as Democrats like Clinton, Obama and John Kerry, has a bit more red-state appeal than other recent Democratic nominees have. Overall, the red state polls imply that Biden has a 12-point national lead (!) if you’re using 2016 as a baseline, or a 9.8 lead if you’re using 2012 instead.

How about polls in deeply blue states? Most of these states actually haven’t been polled very much, but of the ones that have, California stands out:

What blue state polls say about the national race

Biden’s polling lead or deficit in traditionally Democratic states, and what that means for his national margin, based on 2016 and 2012 results

Biden national margin
State Biden’s current lead or deficit* Based on 2016 results Based on 2012 results
Connecticut +20.7 +9.2 +7.2
New Jersey +19.1 +7.2 +5.2
Washington +24.4 +10.8 +13.5
New York +26.8 +6.4 +2.5
Massachusetts +34.1 +9.0 +14.8
California +29.3 +1.4 +10.1
Average (weighted by turnout) +27.1 +5.2 +8.5

*Based on FiveThirtyEight polling averages as of 4:10 p.m. Eastern on Sept. 23. States are included only if they have at least five total polls or polls from at least three pollsters. Sorted from reddest to bluest.

Biden is leading by “only” 29.3 percentage points there, which, of course, is a very large lead, but he is actually slightly down from Clinton’s 30.1-point win there in 2016. It makes some sense, though. Biden’s strength relative to Clinton is with older white voters, whereas California voters are majority-minority and young. Then again, that 29.3-point margin would still be higher than Obama’s margins there in 2012 — or in 2008. In total, the blue states imply a 5.2-point national lead for Biden using 2016 as a baseline, or 8.5 points using 2012.

Add it all up, and the state polls are a tiny bit better for Biden than his national polls show — but only a tiny bit.

The results from red, purple and blue states combined3 imply that Biden is ahead by 8.0 percentage points nationally (you get the same results whether using 2012 or 2016 as a baseline) as compared with his current 7.3-point lead in national polls.

Perhaps the broader lesson here is that we don’t really need national polls for all that much.

In fact, our model uses them fairly sparingly.4 The election is contested at the state level. Although it can be useful to know where the national popular vote stands for various reasons, you don’t actually need national polls to forecast it — you can come up with pretty good (indeed, often better) estimates of the national popular vote by using state polls instead.

Footnotes

  1. FiveThirtyEight is a part of ABC News.

  2. Defined as the state having at least five total polls, or polls from at least three pollsters.

  3. In this calculation, I’m weighting based on each state’s turnout, and not simply averaging red, blue and purple states together.

  4. The exception mostly being to calculate what we call a “timeline” adjustment in states that haven’t been polled that much recently.

Nate Silver is the founder and editor in chief of FiveThirtyEight.

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