From Straight Arrow · · 2m
Why polls and markets got midterms right but margins wrong
Polls and markets correctly predicted midterm winners but underestimated margins in close races.
In brief
Polls and markets correctly predicted midterm winners but underestimated margins in close races. Democrats won the House by 13 percentage points despite polls showing only 9, with Texas and South Carolina races flipping. Originally reported by Straight Arrow.
Polls predicted Democratic House win
Polls before Tuesday’s midterms showed Democrats winning the national House vote by about 9 percentage points.
Democrats won by 13 percentage points
As of Thursday afternoon, they’re on track to win by about 13.
Texas and South Carolina races flipped
In Texas’ governor’s race and South Carolina’s Senate race, polling averages favored Republicans, and Democrats won both.
Polling fixes created new problem
The fixes pollsters made after Trump-era misses may have created a new problem, and prediction markets largely followed the polls into it.
Polling response rates dropped
In 1997, about 36% of people contacted for Pew Research Center phone surveys responded. Now, response rates are down to 1% or 2%.
Polling bias toward Democrats
In 2020, Democrats were 3 percentage points more likely than Republicans to cooperate with pollsters.
Polling weighting adjustments
Pollsters correct for that with weighting, counting some answers more heavily than others.
2024 polling changes
By 2024, many pollsters had also started asking respondents whom they voted for in the last presidential election, then adjusting their samples to match the actual results.
Texas governor race outcome
Kalshi gave Republican Gov. Greg Abbott about a 60% chance of winning on Election Day. He lost to Democratic state Rep. Gina Hinojosa by 7.1 percentage points.
South Carolina Senate race outcome
In South Carolina, markets gave Republican Sen. Darlene Graham about a 70% chance of keeping her seat. The polling average had her up 2.6 percentage points. Democrat Annie Andrews won by 4.4.
2028 presidential race test
Pollsters face a bigger test in 2028. They’ll need to better model who will vote and how people recall their past votes.
The main idea
Democrats won the House by 13 percentage points despite polls showing only 9, with Texas and South Carolina races flipping.
