Polling stations are once again facing one of the great uncertainties of American politics this Tuesday: are they correctly managing to measure electoral support for the Republican Party or is there a portion of its voters that is not sufficiently reflected in the surveys?
The question takes on special importance in midterm elections, where small differences within a small group of districts can determine which party controls the House of Representatives and the Senate.
The problem is not new. Since Donald Trump’s first presidential victory, in 2016, American polling firms have had difficulties in capturing certain segments of the Republican electorate.
However, methodological studies also warn that not all polling errors respond to the same causes, nor can they be automatically extrapolated from one election to another.
Why some Republican voters participate less in polls
A report published by Pew Research Center on September 16 of last year explains that there is growing evidence that Republicans have shown a slightly lower tendency than Democrats to participate in certain polls, especially during presidential elections.
This difference can lead to what specialists call partisan nonresponse bias.
The phenomenon appears when the people who agree to answer a survey have political preferences different from those who refuse to participate and the statistical adjustments fail to fully compensate for that difference.
In that case, the sample may reflect a distribution of votes that does not match that of the electorate as a whole.
Pew links this problem to some of the difficulties that polls experienced in estimating support for Trump and other Republican candidates in 2016, 2020 and 2024.
The problem does not affect all elections in the same way
Researchers also introduce an important distinction: measurement errors associated with the Republican electorate were less severe in the 2018 and 2022 midterm elections than in some presidential elections.
This means that there is no rule according to which polls must necessarily underestimate Republicans in any given election.
Moreover, territorial differences are fundamental. The participation of rural, urban, and suburban voters can change from one election to another, as can the composition of the electorate that ultimately goes to the polls.
The hypothesis that many rural Republicans refuse to respond because they are angry with pollsters seems plausible as a partial explanation for some behaviors, but it cannot be taken as proven for the 2026 elections without specific studies that identify that motivation.
Polls are finding it increasingly difficult to get responses
Pew Research Center warns that one of the main problems of U.S. polling is the decline in participation rates.
In the center’s own telephone surveys, the proportion of people who responded fell from 36% in 1997 to single-digit percentages in the most recent years of the series studied.
The 2022 telephone poll by The New York Times and Siena, cited by Pew, achieved a response rate of 0.4%.
This does not mean that a poll with few responses is necessarily incorrect. Its accuracy also depends on how the sample is selected, the information available about the participants, and the statistical adjustments applied.
However, the more difficult it becomes to contact voters, the greater the risk that those who agree to participate do not adequately reflect the overall population.
How pollsters try to correct the problem
To reduce these errors, numerous institutes incorporate weights based on political characteristics, such as party identification or recall of voting in previous elections.
These techniques seek to correct imbalances between the survey participants and the estimated composition of the electorate.
However, they do not completely eliminate uncertainty either. If the actual participation of certain groups changes or if people who do not respond have different behaviors from those who do, deviations can persist.
Therefore, national estimates should be interpreted together with territorial data, especially in elections where each district of the House of Representatives and each state with Senate seats votes independently.
The response will come with the scrutiny
The first hours of the count will make it possible to compare the previous estimates with the actual results, although it will be necessary to wait until enough votes have been counted before drawing conclusions.
A difference between polls and results would also not automatically prove the existence of a hidden Republican vote. It could be due to changes in turnout, estimation errors, last-minute shifts, or peculiarities of the electoral system.
The big question tonight is not only which party gets more votes, but to what extent the polls have managed to correctly identify those who ultimately went to the polls.