Donald Trump’s resounding victory in the 2024 Iowa caucuses should have been expected by just about everyone. You could have seen it coming based on his fundraising numbers, his campaign’s presence in the state, his refusal to debate his primary opponents — or you could have looked at just about any poll.
Since 2016 (and 2020), however, there’s been some apprehension about trusting polls. And even though the state-level polls were generally more accurate in the 2022 midterms than conventional wisdom holds, recent discourse about national polling of a Trump-Biden rematch has reignited those concerns.
Trump led the Republican field for the last year, hovering at about 50 percent in most polls in Iowa as far back as May 2023. And his final vote share, of 51 percent of the vote, is right in line with what most polls expected. And it’s not just Trump. Once all the votes were counted, it looks like the polling of Iowa was pretty accurate in the runup to Monday night’s caucuses. The topline numbers are nearly identical to the final results. And for that to be true in Iowa, with its fickle weather, low turnout, and tedious caucus system, is a victory for pollsters, despite the widespread skepticism over public polling since 2016.
Primary polling across the country historically tends to be pretty inaccurate, G. Elliott Morris, a data journalist and the editorial director of data analytics at ABC News’s FiveThirtyEight, told me. “Not just in Iowa, but they tend to be off on average 7 points. So for any given candidate, their vote share is 7 points different from their polls, going back to 1999 or so. In reality, it might be a bit bigger.”
But looking at the mean average error (MAE), the average disparity between the polls and the final results, for the top three candidates — Trump, Florida Gov. Ron DeSantis, and former South Carolina Gov. Nikki Haley — that gap was just 2.3 points, by Morris’s calculations. “You can round that down to 2 if you…
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