Trends and Noise

In my efforts to keep up with what’s going on politically in Iowa (essential in presidential cycles, and in this particular midterm), I rely to some extent on the Des Moines Register. But since the Register’s gone to a metered subscription model, and I’m resisting yet another subscription payment, I rely more on two more partisan sources: The Iowa Republican and Bleeding Heartland. The first is often too over-the-top to be useful (particularly when Kevin Hall is writing), but occasionally has nuggets, particularly during GOP primaries; the latter is more objective if unapologetically progressive. And today desmoinesdem of Bleeding Heartland has a small but important insight about following 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?

So yeah, it gets tricky. We should look at trends between polls from the same source other than comparing apples and oranges, but any one poll could be an outlier. Best to stick with averages when possible.

Ed Kilgore

Ed Kilgore, a Monthly contributing editor, is a columnist for the Daily Intelligencer, New York magazine’s politics blog, and the managing editor for the Democratic Strategist.