Polls largely underestimated Zohran Mamdani’s support in the Democratic primary for the New York City mayor, illustrating once again just how difficult it can be to accurately poll primary elections.
When polling general elections, pollsters are helped by the fact that increasing polarization has led Americans to sort neatly into their political camps, with more than 90 percent of partisans supporting their party’s candidate. But in primary elections, partisanship no longer factors into voters’ decisions in the same way. Voters’ preferences are more fluid in partisan primaries and more difficult to track over time.
Primaries also tend to be much more volatile than general elections, making the timeliness of a poll more relevant. In the run-up to the 2016 presidential election, nearly every Republican contender in the field took a turn as the front-runner in the polls before Donald J. Trump ultimately pulled ahead. And in the 2020 Democratic primary, Elizabeth Warren, Joseph R. Biden Jr., and Bernie Sanders ping-ponged in the polls.
The New York City mayoral primary presents an additional challenge because of its use of ranked-choice voting. Pollsters took different approaches to try to mirror the process, but it is challenging to accurately simulate what voters actually experience at the ballot box.
While most polls did not show Mr. Mamdani leading in the first round of balloting, they did appear to show him gaining support in the final weeks of the campaign.
Polls in March and April of this year showed former Governor Andrew Cuomo ahead by 20 to 30 percentage points. Surveys conducted in May and June showed Mr. Mamdani cutting that lead down, often to single digits. And an Emerson College poll taken within a week of the election found Mr. Mamdani neck and neck in the first round and winning in the final round of voting.
Ruth Igielnik is a Times polling editor who conducts polls and analyzes and reports on the results.
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