11 October 2020
Two new polls: is either right?
Emerson reports Daines leads Bullock by 9 points —
but Data for Progress reports Bullock leads by a point
Two online polls of likely Montana voters were released last week. One, by Emerson College, reports Republican Sen. Steve Daines has a nine point lead over Democrat Gov. Steve Bullock. The other, by Data for Progress, reports Bullock has a one-point lead.
The integrity intervals (comparable to an MOE) are 4.3 percent for Emerson, 3.6 percent for DFP, a 7.9 percent separation.
Emerson also reported Trump leads Biden by 13 percent, and Gianforte leads Cooney by 13 percent. DFP reports Trump has a six point lead over Biden; Gianforte v. Cooney was not polled.
Below two plots of the publicly available post-primary polls of Montana’s U.S. Senate election.
The data also can be presented as a single number: Bullock’s net lead.
Emerson is a consistent outlier. Why? Possibly because of how it weights its sample to match the population’s demographics, the reference demographic set usually being the Census Bureau’s American Community Survey. Emerson chose a different reference: “The data sets were weighted by gender, age, and education based on 2016 voter turnout modeling.” Not placing a comma after “education” makes that sentence ambiguous, but I think Emerson used the turnout modeling for all its weighting, not just for weighting education.
The poll was not weighted for income, and, because Montana is not a register by party state, not weighted for political affiliation.
I think using 2016 voter turnout modeling for weighting instead of the American Community Survey is a dubious concept. Because I have not been able to Emerson’s reasons for employing this weighting scheme, at this time I’m limited to raising a red and question mark flags.
Asking the people polled whether they voted in 2016 and/or 2018 is a useful screen for identifying likely voters.
Approach Emerson’s polls with caution, but do not dismiss them.
Bullock’s campaign has not, to my knowledge, released any of its private polls. Campaigns often release their own polls when their polls show them leading or not nearly as far behind as public polls. If Bullock does not release a poll reporting he’s running neck and neck with Daines, it could be an indication that Emerson’s poll was closer to the mark than DFP’s.
The keys to statewide races in Montana are Trump’s horserace numbers and his approval/favorability numbers. As long as he stays at 50 percent or higher, his coattails may be long enough to pull statewide Republicans across the finish line ahead of their Democratic opponents. If Trump’s number sink below 50 percent, if they end up underwater, Montana's statewide Republican could go down with him.
Bullock and Daines debated Saturday evening. The debate can be viewed online.