Why the Polling in Michigan Was Off the Mark

Much of the pre-election polling in Michigan’s Democratic Senate primary showed Dr. Abdul El-Sayed, a progressive candidate, with a commanding lead over the more moderate Haley Stevens. Come election night, however, Dr. El-Sayed eked out a narrow victory, in a race so tight it was not called until Wednesday morning.

So, why did the polling miss by such a wide margin?

Conducting surveys in partisan primaries has long presented a challenge to pollsters, as it requires them to make assumptions about who will actually turn out to vote. Without mandatory party registration in Michigan, pollsters must guess who will show up on Election Day.

Many surveys assumed political independents would make up 30 to 40 percent of the electorate. These polls showed Dr. El-Sayed winning independents by a wide margin. While there is little authoritative detail available on the actual electorate, that assumption could have contributed to the challenge in polling the race, as voters who decline to identify with a political party tend to vote less frequently.

Another challenge was a lack of high-quality polling. In The New York Times’s poll tracker, “select pollsters” are those who have met qualifications to be considered generally more accurate and trustworthy. In the final month before the primary, just one poll was conducted by such a group.

Much of the remaining polling was conducted by groups that were — either directly or indirectly — affiliated with Dr. El-Sayed’s campaign. Historically, campaigns and their allies have had an incentive to produce polls showing their candidate doing well to try to build a narrative about the race, even if those numbers do not always align with reality.

Polls did seem to understand the underlying dynamics of the race. In pre-election polls, Dr. El-Sayed did particularly well with younger voters; on election night, he performed particularly well in areas with a high concentration of young voters. Polls also accurately captured Ms. Stevens’s strength with Black voters and in suburban communities.

Polls also seemed to accurately capture the mood of the electorate on Israel. Ms. Stevens’s support for Israel — and the support she received from the American Israel Public Affairs Committee — appears to have been a liability. Polls showed that AIPAC, which spent heavily on behalf of Ms. Stevens, had a very negative image among likely Democratic primary voters in the state. Ultimately, that support likely cost her with some voters.