Many factors can explain disparities in poll results

By William Hershey

Dayton Daily News

DAYTON

Independent public opinion polls aim to help voters keep up with heated elections such as Ohio’s governor’s race, but the results may be confusing.

A new Vindicator/Ohio Newspaper poll shows Democratic incumbent Ted Strickland and Republican challenger John Kasich with roughly the same level of statewide support among likely voters — 49 percent for Kasich to 47 percent for Strickland.

The results were close to the same in a CNN/TIME/Opinion Research Group poll released last Wednesday. However, a Quinnipiac University poll released on Tuesday showed Kasich ahead by 10 points. And an earlier Quinnipiac poll had Kasich ahead by as much as 17 points.

What gives?

The first thing to remember when discussing polls is that they are based on probability, not certainty, said political scientist John Green, director of the Bliss Institute of Applied Politics at the University of Akron.

Polls use a scientific, randomly drawn sample aimed at representing the outcome of what would happen if everyone in a group — such as all likely voters in a state — were questioned.

Even if the same organization did the same poll on the same day, the results wouldn’t always be the same, said Green.

The range of possible results often is referred to as a poll’s margin of error. Pollsters often say the results would fall within the poll’s margin of error 95 percent of the time.

In the new Vindicator/Ohio Newspaper poll, the margin of error is plus or minus 3.3 percentage points in 95 out of 100 cases.

The margin of error is just one possible source of inaccuracy in polls.

Others include lack of proper training by interviewers, flawed wording of questions and the order in which questions are asked, write Sheldon R. Gawiser and G. Evans Witt in their book, “20 Questions a Journalist Should Ask About Poll Results.” Also, while most polls on the governor’s race refer to “likely voters,” there’s no ‘generally accepted way to define likely voters,’ said Green.

“Different people do it in different ways,” he said. “Pollsters almost get into fistfights over how to measure likely voters.”

For the Vindicator/Ohio Newspaper Poll, likely voters were determined by people who said they were most interested in the election and who said they were going to vote, said Eric Rademacher, co-director of the University of Cincinnati’s Institute for Public Research.