Systematic Errors in 2010 Polls?

With the midterms a few days away, lemme go out on a limb and say that I don’t think it’ll be *that* bad for Democrats. Oh sure, it’ll suck. Dems spent the last two elections winning in districts that are really conservative, so it’s only natural that many of those seats would swing back to the GOP as the result of 2010′s Tea Party Hate-A-Thon.

But I don’t think the GOP is a lock to win more than 50 House seats or that the Democrats have a less than 20% chance of holding onto the House. Based on what Nate Silver recently wrote, I think it’s looking more like a 50-50 shot :

But suppose that our forecast is biased against the Democrats by one point across the country as a whole, perhaps because pollsters are overestimating the enthusiasm gap very slightly. Just one point. Well, there are 6 seats in which we have the Republican candidate projected to win by less than 1 full point (it might be a very long election night, by the way). If Democrats hold those 6 seats, the projected Republican gains would be down to 46.

Now suppose that the forecast understates Democratic support by 2 points. There are 8 seats in which we project the Republican candidate to win by a margin of between 1 and 2 points; now these would also be wiped off the board. Now the Republican gains would be reduced to just 38 seats — and the Democrats would hold the House, 218-217!

Read that again: it means that if our forecasts turn out to be biased against Democrats by just 2 points overall, the party becomes about an even-money bet to hold the House.

And where might those two points come from? Well, first there’s the cell-phone problem :

The latest estimates of telephone coverage by the National Center for Health Statistics found that a quarter of U.S. households have only a cell phone and cannot be reached by a landline telephone. Cell-only adults are demographically and politically different from those who live in landline households; as a result, election polls that rely only on landline samples may be biased. Although some survey organizations now include cell phones in their samples, many — including virtually all of the automated polls — do not include interviews with people on their cell phones.
. . .
In three of four election polls conducted since the spring of this year, estimates from the landline samples alone produced slightly more support for Republican candidates and less support for Democratic candidates, resulting in differences of four to six points in the margin.

It makes sense that this might underestimate Democratic support since cell-only households tend to be younger, more educated, and urban than those with landlines. Adding to this problem is that some polls, like this one for the Nevada Senate race from CNN, are just undercounting Democratic-leaning demographics entirely :

At the end of the day, it’s all going to be about who’s more motivated to go vote, but I won’t be surprised if the big story next week is about how the media used bad polls to drive a bogus narrative.

2 thoughts on “Systematic Errors in 2010 Polls?

  1. It has been hard to watch the news on any of the channels without Obama Bashing or On the verge of *WAVE* of the destruction of *THE DEMOCRATS* I have never seen such a disgraceful attempt to screw up and election & screw the MIDDLE CLASS.
    Greg, keep up your going out on a limb & letting the American People know the Real Truth!

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