DataLab

Republican candidates typically poll better among likely voters, particularly in midterm elections when Democratic-leaning constituencies are less likely to turn out. This fact of Americans politics is why a poll released in Wisconsin on Wednesday was so weird.

According to the latest Marquette University Law School poll, Wisconsin’s Republican governor, Scott Walker, is losing his re-election bid against Democrat Mary Burke by 2 percentage points among likely voters but winning by 3 points among registered voters.

Which is right?

Chances are, the results from the registered voter sample are closer to the truth — Walker is probably slightly ahead. The poll’s registered voter results are more in line with the long-term averages of the Marquette poll and Wisconsin polls overall, and there isn’t evidence from past campaigns that Marquette’s likely voter screen produces more accurate results.

As has been documented over and over again, Wisconsin politics are ultra polarized. Voters either love or hate Walker. His approval rating has been between 47 and 51 percent in every Marquette poll from January 2012 to August 2014. Walker won the governorship by 5.8 percentage points in 2010 and won a recall election by 6.8 points in 2012.

There hasn’t been a lot of movement in the 2014 gubernatorial election either. The first Marquette poll, taken in October, had Walker up 47.1 percent to Burke’s 44.9 percent among registered voters — nearly identical to this month’s Marquette survey. In all six Marquette surveys taken since October, Walker leads Burke by an average of 3.4 percentage points among registered voters.

Of course, it’s possible the registered voter results are missing something. Maybe there is a turnout gap in favor of Burke. But we would expect to see evidence of this Democratic enthusiasm in the candidates’ fundraising numbers. Yet Walker is outraising Burke among individual Wisconsinites in two ways.

First, he has raised $4.4 million in individual donations since the beginning of the year from in-state donors. Burke has raised only$2.6 million. Second, if we look at the number of contributors living in Wisconsin, Walker is ahead: 21,254 residents have given to his campaign since Jan. 1; 19,383 have given to Burke. The gap between the total number contributors is smaller than money raised, but it doesn’t match the most recent Marquette poll suggesting that Burke’s supporters are more enthusiastic than Walker’s.

Moreover, the five Marquette polls this year haven’t shown a consistent edge for Burke among likely voters. In three of the surveys, Burke did better among likely voters than among registered voters. But in two, and as late as May, she did better among registered voters.

The average of all likely voter results from Marquette since the beginning of the year puts Walker up by 3.3 percentage points over Burke. That looks a lot like the average of registered voter results, doesn’t it?

It’s important to remember there is nothing magical about a likely voter screen. Marquette chooses a simple screen: Those who say they are absolutely certain to vote in November. Marquette could just as easily choose to include participants who say they are very likely to vote. Both methods have been employed in the past by other polls, and studies have shown that some people don’t accurately gauge their likeliness to vote.

Nor is there much of a sign that using a likely voter screen on Marquette’s surveys improves their accuracy, even within a month of the election. An average of Marquette polls during the final month of the 2012 recall had Walker ahead by 6.4 percentage points among registered voters and 6.5 points among likely voters. Walker won by 6.8 points. In the final month of the 2012 presidential campaign, President Obama led Mitt Romney by an average of 4.2 percentage points among likely voters and 6.9 points among registered voters. Obama won the state by 6.9 points.

Given all this information, I’m inclined to focus more on the registered voter result that shows Walker slightly ahead. That doesn’t mean he’ll win. A 3-point lead at this point indicates that the race is too close to call. Still, Walker (as the Huffington Post Pollster aggregate shows) is a slight favorite.

Never miss the best of FiveThirtyEight.

Subscribe to the FiveThirtyEight Newsletter
×

Sign up for our newsletters to keep up with our favorite articles, charts and regressions. We have two on offer: The first is a curated digest of the best of what’s run on FiveThirtyEight that week. The other is Ctrl + , our weekly look at the best data journalism from around the web. Enter your email below, and we’ll be in touch.

By clicking subscribe, you agree to the FanBridge Privacy Policy