Recent polls in the seven swing core states show a stunningly close presidential race: 124 of the last 321 polls taken in those states — nearly 39 percent — show margins of 1 percentage point or less.

In fact, state polls show not just a stunningly close race, but an improbably close one. Even in a truly equal election, the randomness inherent in polls would produce more varied and less clustered results—unless state polls and poll averages are artificially close because of decisions the polls make.

The results of a poll depend on the opinions of the voters and the decisions of the polls. Decisions about how to weight polls to match the expected composition of the electorate can move poll results up to 8 points. This is true even if researchers make perfectly reasonable decisions about how they weight their survey data, because survey researchers have been forced to consider new methods and ideas for weighting and dealing with declining response rates from missed surveys in 2016 and 2020.

But the fact that so many polls are reporting exactly the same margins and results raises a troubling possibility: that some pollsters are making adjustments in such similar ways that those choices are skewing the results, creating a potential illusion of certainty — or that some researchers they even look at the results of others to guide their own (ie, “the herd”).

If so, the artificial similarity of the polls can create a false impression that may not show on election day. We could be in for a very close election. But there’s also a significant chance that one candidate or another will sweep every swing state and win the presidency somewhat comfortably, at least compared to the balanced picture in the polls.

What should we see in a perfect world of polls due to randomness?

In a perfect polling world—a researcher’s paradise where every voter can be contacted and every voter contacted responds—we can use math to calculate how much variation there should be because voters are randomly selected to take a survey

If a race in this world were truly tied 50%-50%, the polls wouldn’t all produce 50%-50% results. Imagine if the pollsters of this world conducted 100 identical polls of 863 randomly chosen voters (that’s the average sample size of this year’s swing state polls). Results from 95 of those polls would show the candidates getting support somewhere in the 46.7 percent to 53.3 percent range — even though we know in this imaginary world that the race is actually tied at 50 percent. The other five polls would show candidates winning something even higher or lower outside that range.

This variation is known as the “margin of error” in a poll—that is, how much the random selection of voters who always respond can affect a poll’s estimate for a candidate.

Because each candidate’s support varies randomly, these polls predict a margin in a close race that ranges from -6.6 to +6.6 for 95 out of 100 polls (with even larger margins for the other five).

It’s important to point out that the range of margins we can expect in a close race (and in a perfect polling world) is much larger than swing state margins in 2020. Even under ideal voting circumstancesit is difficult, if not impossible, for a poll to be very informative about who is leading a close race. And this is arguably a lower bound of what we should see in the messier real world, where polls vary in how respondents are selected, contacted and weighted to match the electorate they think they will have results in 2024.

We can also calculate what share of polls of 863 people we should expect to show different margins in a truly even race. Rounded to the nearest percentage point, about 11% of polls in a tied race should show a tie.

That means that almost 9 out of 10 polls of a tied race should not actually show a tie, due to randomness and margin of error.

About 32% of polls should have a margin of 1 point or closer, 55% should have a margin of 2 points or closer, and 69% should have a margin of 3 points or closer. Even in a 50-50 race, about 10% of polls should have a margin of more than 5 points due to inherent randomness – almost the same percentage that shows a tie (rounded)!

With enough polls, the predicted margin should also resemble a “bell curve” normal distribution—with a similar number of polls showing either candidate leading.

What are we seeing in the swing state polls?

Actual polls of swing states show much less variation than the benchmarks we would expect in a perfect polling world. Of the 321 polls in the seven swing states, only 9 polls (3%) report a margin greater than 5 points. Even if every race were even—which they are not—we would still expect to see about 32 of the 321 polls with a margin of more than 5 points due to randomness.

Viewing how reported voting margins compare to what we would expect in a perfect polling world strongly suggests “aggregation” of variable state voting margins around statewide voting averages. In these 321 state polls, 69 of them (21%) report an exact tie and 124 polls (39%) report a margin that is 1 percentage point or less. Both figures are roughly double what we would expect in a perfect polling world where the only source of variation is the random selection of voters who respond.

Pennsylvania is perhaps the most disturbing state. 20 of 59 polls there (34%) show an exact tie and 26 (44%) show a margin of 1 point or less And even though there’s a 15% chance that a truly tied race could produce a poll with more than a 5-point margin due to randomness, we see only 2 of 59 Pennsylvania polls (3.3%) with a greater than 5-point margin.

Even where the poll results are not so tightly clustered, such as in Arizona, Michigan, and Wisconsin, there are still many more polls than one would expect around the poll average and too few polls by large margins.

what’s going on

The concentrated margins we see in swing state polls likely reflect one of two possibilities.

One possibility is that pollsters sometimes adjust a survey result that seems “strange” to them by choosing a weighting scheme that produces results closer to the results of other surveys. There appear to be strong incentives for surveyors who attest to risk to do so. Unless a pollster conducts a lot of polls and can be sure that the impact of randomness averages out, they may fear the reputational and financial costs of getting a wrong result due to randomness, because pollsters are judged on the accuracy of their polls .

A risk-taking poll that gets a 5-point margin in a race it sees as tied may choose to “adjust” the results to something closer to what other polls show, lest their outlier poll tarnish their reputation relative to competitors.

Another, more likely possibility is that some of the tools pollsters use in 2024 to address 2020 polling issues, such as weighting by partisanship, past voting or other factors, could smooth out differences and reduce variation in reported poll results. The effect of such decisions is subtle but important because it means that the similarity of the polls is determined by the decisions of the pollsters rather than the voters.

And if those assumptions are wrong, something that is unknowable until after the election, then the risk of a potentially significant polling error increases as the variation between different polls decreases.

Why this matters

That so many swing state polls report similarly close margins is a problem because it raises questions about whether the polls are tied in these races because of voters or pollsters. Will 2024 be as close to 2020 because our politics are stable, or will the 2024 polls just look like 2020 results because of the decisions the state polls make? The fact that the polls seem more tightly clustered than we would expect in a perfect polling world raises serious questions about the second scenario.

The reported polls and polling averages create a consensus that the race will be very close and we are likely to see a result similar to 2020. Maybe that is true. It would be great if the polls successfully address the concerns of 2016 and 2020 in 2024.

But the fact that all polls report such similar margins doesn’t necessarily make those margins more likely to represent the bottom line. In fact, it raises the possibility that the election results could be unexpectedly different from the proximate narrative that the state polling pool and polling averages suggest.