What’s on your mind this weekend, Bleeding Heartland readers? This is an open thread.
I’ve been reading about opinion polls, and specifically, the polling industry’s growing challenge of sampling a group that looks like the electorate. Almost every day, a new poll appears on Iowa’s U.S. Senate race. Since last weekend’s Selzer poll for the Des Moines Register and Bloomberg News, which showed Ernst up by 1 point, three other polls have shown small leads for Ernst, while one showed Braley slightly ahead. How Iowa’s no-party voters are leaning is anyone’s guess; some polls have shown Ernst leading among independents, others have indicated that Braley is ahead.
All of these surveys are reporting results among “likely Iowa voters,” but which, if any, have correctly identified a representative sample? The statistical margin of error means little if the pollster is systematically oversampling certain voters while not reaching other groups. As Nate Silver discusses here, data since 1998 show that polls of U.S. Senate or gubernatorial races are less accurate than presidential polls.
Media orthodoxy says reporters and pollsters can never admit their own organization’s poll might have been an “outlier.” Rather, readers are told that all trends apparent from some group’s poll reflect real shifts of public opinion. So we get the Des Moines Register’s Jennifer Jacobs saying Braley “has begun to overcome some of the vulnerabilities detected in the Iowa Poll two weeks ago,” going from a double-digit deficit among independents to a slight lead, and going from 25 points down among male respondents to 16 points down. Really, is it likely Braley surged so much in two weeks, as opposed to the previous Des Moines Register/Selzer poll overstating Ernst’s advantage overall and among certain groups?
Similarly, Quinnipiac’s latest Iowa poll shows “independent voters backing Rep. Braley 48 – 43 percent, a shift from Ernst’s 50 – 43 percent lead among these key voters last month.” Did no-party voters really change their minds in large numbers over a few weeks, or did Quinnipiac’s findings change because of statistical noise?
After the jump I’ve posted excerpts from several articles about polling and some revealing comments by Ann Selzer, a guest on a recent edition of Iowa Public Television’s “Iowa Press” program.
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