Accuracy of political polls; understanding how they work

Political polls

LA CROSSE, Wis. (WKBT) – A new Wisconsin poll shows Sen. Bernie Sanders in the lead among likely primary voters. However, many people question the accuracy of polls, especially after the 2016 presidential election.

Election momentum for Senator Bernie Sanders continues after a comfortable win in the Nevada caucuses. Sanders now finds himself polling on top among Wisconsin democratic voters. How accurate are all of these polls? Especially after 2016 proved many polls wrong.

“There are always a number of undecided voters in polls,” said political science expert Joe Heim.

Heim said undecided votes are difficult to gauge.

“The last week three out of four people who voted who were undecided went with Trump,” Heim said.

In 2016 only four out of 67 national polls had Trump in the lead from the start of October leading up to the election according to

“Primary polls have had a history of being incorrect,” Heim said.

Heim said people need to understand the nature of polls to uncover bias.

“When you do a survey correctly if you have seven or eight democrats to mention you don’t mention them in a certain order,” Heim said. “You rotate those.”

Everything from who paid for the poll, who was asked, sample size and when they were asked all matter. Some polls only look at registered voters or likely primary voters. Some polls are done only online.

“There are a lot of little techniques with polling and it’s kind of a tricky business,” Heim said.

Plus there is a margin of error to consider. If candidate A has 53 percent support compared to 47 for B with a margin of error of three percent, it’s a tie within the margin of error.

The Wisconsin State Journal looked at elections from 2008 through 2016 and a couple of different Wisconsin polls were pretty accurate with exception to 2016.

“The gold standard in Wisconsin has been the Marquette Law School Poll,” Heim said. “It’s been generally one of the most accurate ones.”

Heim said polls behave like our Midwest weather. They do not always represent what voters will do on election day.

“It’s not predictive,” Heim said. It’s a snapshot in time and people change their minds in a week or two.”

Heim said many Trump voters were not truthful on who they were going to vote for in 2016. A lot of attention will be on Wisconsin. The state is a toss-up between Trump and no matter who wins the Democratic nomination at this point.