The wide divergence between election results and the Marquette Law School poll in the Wisconsin Democratic Primary Aug. 11 has been subject to scrutiny, including by the poll director Charles Franklin.
In a blog post, Franklin said the race was complicated with candidates dropping out late after voting had started, one candidate re-entering the race late and an unprecedented endorsement by sitting Governor Tony Evers.
In the Marquette Law School Poll’s final survey of Wisconsin voters, July 22-27, Francesca Hong received 38%. Her unofficial vote total in the August 11 primary election is 39.3%. And 34% said they were undecided.
“The remarkable difference between poll and outcome was that the poll had David Crowley at 7% and he won with 39.8%. Mandela Barnes, who dropped out three days after the poll was completed, had 16% in the final survey. One clear thing is that the vast majority of late-deciding voters went to Crowley and very few went to Hong,” Franklin wrote.
In addition to late changes, Franklin said non-response bias is always a potential source of error in polls.
“In this case, the age and ideological makeup of the survey samples of primary voters was similar to the pre-primary makeup of Democrats, suggesting that young, very liberal, Hong supporters were not overrepresented. Those groups strongly supported her but were not an unusually large share of the samples. Older and moderate voters were more undecided and less supportive of Hong in both of our July polls but had not settled on the very newly returned Crowley at the time of the last survey.”
And Hong’s actual vote of 39% was barely different from her 38% in the final poll, further demonstrating that her supporters were not overrepresented in the survey.
Turnout was much larger than in recent Democratic primary contests: an unofficial 792,009, compared to 640,247 in the 2024 Senate primary and 538,857 in the 2018 gubernatorial primary.
