In three earlier posts—most recently here—I analyzed all polls conducted by Emerson College (“Emerson”) of 2020 presidential, senatorial and gubernatorial elections. I found that they had a clear bias towards the Republican candidate, on average, compared to all other polls of the same election.
As I continue to analyze polls of the presidential election between former Vice President Joseph R. Biden, Jr. and President Donald J. Trump, as well as this year’s 35 Senate and 11 gubernatorial elections, I have observed the opposite mathematical bias for Quinnipiac University (“Quinnipiac”) polls.
In fact, as we will see, the two polling organizations nearly mirror each other in their mathematical bias.
Let us begin with the national race between Democrat Biden and Republican Trump. Using all 632 publicly-available polls released since January 1, 2019, I calculated a weighted-adjusted polling average (WAPA) of 8.3. That is, adjusting for time (with polls conducted after August 29 weighted and additional 1.5 times higher and polls conducted since September 29 3.0 times higher), pollster quality and partisan lean, Biden leads Trump by a little over eight points nationally. Emerson has an A- rating, and a historic lean of 0.3 points Democratic, while Quinnipiac has a B+ rating, and a historic lean of 0.2 points Democratic.
Table 1: State-level 2020 presidential election polling averages by Emerson College and Quinnipiac University compared to all other pollsters in the same state
|AVERAGE All States||3.5||-0.5|
|AVERAGE Ohio, Pennsylvania, Texas||1.9||-0.7|
However, using the same calculation method—except for ignoring partisan lean—the 20 Emerson polls conducted by Emerson give Biden “only” a 3.7-point lead, which is 5.3 points more Republican than the average of the other 612 polls. At the same time, the 13 Quinnipiac polls give Biden a 9.9-point lead, which is 1.0 points more Democratic than the average of the other 619 polls. Put another way, Quinnipiac polls “see” a race that is 6.3 points more favorable to Biden than Emerson polls do, though both give Biden a solid lead.
While national polls are interesting—and plentiful—it is the Electoral College that determines who wins presidential elections. Table 1 compares state-level presidential polling averages by Emerson and Quinnipiac, in states where they have assessed the presidential election at least twice, to those calculated by all other pollsters in the state; positive values indicate a Democratic lead or pro-Democratic bias, and negative values indicate the opposite. Emerson has conducted one poll of the presidential election in Florida, Georgia, New Mexico, New Jersey and South Carolina; Quinnipiac has conducted one poll of the presidential election in Colorado, Connecticut, Iowa, Michigan, New Jersey, New York and Wisconsin.
In the 13 states where Emerson has assessed the 2020 presidential election, the average bias is only 0.5 points towards Trump, fully 4.8 points lower than its national bias toward Trump. By contrast, in the eight states where Quinnipiac has assessed this election—five of them in the south, the average bias is 3.5 points toward Biden, 2.5 points higher than its national bias toward Biden. The gap between the two polling organizations also narrows from 6.3 to 4.0 points at the state level.
Notably, while Quinnipiac has an average bias toward Biden in all eight states—ranging from more than five points in Georgia, Maine and Florida to around one point in Ohio and Texas—Emerson’s bias is evenly split across its 13 multiple-assessment states, ranging from nearly six points towards Trump in the western states of Montana and Nevada to between two and four points toward Biden in the disparate states of Arizona, Massachusetts (where Emerson College is located) and Michigan.
Curiously, Emerson and Quinnipiac have both assessed the 2020 presidential election in only three states—Ohio, Pennsylvania and Texas—multiple times since January 1, 2019. In these three states, the bias is relatively narrow: Trump +0.7 for Emerson and Biden +1.9 for Quinnipiac, for a gap of “only” 2.6 points.
Turning to other statewide elections in 2020, Table 2 compares Senate election polling averages by Emerson and Quinnipiac, in states where they have conducted such polls at least twice since January 1, 2020, to those calculated by all other pollsters in the state. Emerson has conducted one Senate election poll in Georgia, assessing both seats on the ballot this year, as well as in Arizona, Iowa, Michigan, Minnesota, New Hampshire and New Jersey; Quinnipiac has conducted one Senate election poll in Iowa and Michigan. For the “jungle primary” in which Georgia Republican Senator Kelly Loeffler seeks reelection, I analyze the difference between the total percentage for all Democratic candidates and the total percentage for all Republican candidates.
Table 2: 2020 Senate and gubernatorial election polling averages by Emerson College and Quinnipiac University compared to all other pollsters in the same election
In a reverse of state-level presidential election polling, Quinnipiac has assessed six Senate elections multiple times—again focusing on the south, while Emerson has only assessed Senate elections in Montana and North Carolina more than once; no Senate election has been polled multiple times by both pollsters. Quinnipiac has an average 3.3-point bias toward Democratic Senate nominees, nearly identical to its 3.5-point state-level presidential election bias. By contrast, albeit only in two Republican-leaning states, Emerson has an average 5.0-point bias toward the Republican Senate nominees, nearly identical to their Trump bias nationally, and fully 4.5 points higher than their state-level bias toward Trump. Overall, and recognizing this is not an apples-to-apples comparison, Quinnipiac Senate election polls lean 8.3 points more Democratic than Emerson Senate election polls.
Quinnipiac has been especially Democratic-leaning in Georgia’s two Senate elections, with average pro-Democratic-nominee biases of 6.2 and 7.2 points, and in Maine, while they have shown minimal bias in Kentucky and Texas. As with the presidential election, meanwhile, Emerson has a whopping 7.6-point bias toward incumbent Montana Republican Senator Steve Daines in his race against Democratic Governor Steve Bullock; they are relatively closer to the mark in North Carolina, where Democrat Cal Cunningham has a small lead against incumbent Republican Thom Tillis.
Quinnipiac has conducted no gubernatorial election polls this year, while Emerson has conducted one poll in New Hampshire and multiple polls in Montana (6.5 points more Republican) and North Carolina (7.4 points more Republican), with a large average pro-Republican bias of 6.9 points!
Table 3 lists the average partisan biases for Emerson and Quinnipiac for each set of races.
Table 3: Average partisan biases in Emerson College and Quinnipiac University polls across multiple election categories
While Quinnipiac has had only a relatively small pro-Biden bias in national polls, they have had an overall lean of 2.6 points Democratic across all elections they have assessed multiple times. By contrast, while Emerson has been very close to the all-polls average in their state-level presidential election polling, they have had an overall lean of 4.4 points Republican across all elections they have assessed multiple times. Overall, Quinnipiac has leaned fully 7.0 points more Democratic than Emerson has.
I will not attempt to “explain” these relative partisan biases, though they almost certainly result from some combination of how the demographic distribution of the likely 2020 electorate is modeled, the fact Quinnipiac shifted to “likely voters” models more recently than Emerson did, how hard they “push” initially undecided voters to choose one candidate, and the relative partisan leanings of demographic categories within their respective samples.
I will say, though, that the final Democratic-minus-Republican margin will almost certainly be very close to the midpoint of the two polling averages plus one point Democratic—at least in elections assessed at least once by Emerson and by Quinnipiac.
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