Why I’ve given up on polls

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There has been a lot of discussion over the past week on polls and why polling for the 2014 elections was so bad. As Sean Trende of RealClearPolitics said:

As Tuesday night got going, most people suspected that Republicans were headed for a good night. This, after all, was what the polls strongly suggested. Instead, they had a great night.

What is odd is that, while there was a cluster of conversations suggesting we might see Republican gains of around six-to-eight Senate seats, six-to-nine House seats and the loss of a few governorships — and a secondary cluster analyzing why Republicans might be disappointed (mostly citing the possibility that polls could be skewed away from Democrats by demographic undersampling) — there was no cluster of conversations suggesting that the public polls might understate Republican performance. As the New York Times’ Nate Cohn put it: “I’m not aware of any evidence that polls underestimate Republicans. Please show me the data.”

But in the final analysis, Nate Silver of fivethirtyeight.com notes in his post The Polls Were Skewed Toward Democrats the polls were heavily skewed in favor of Democrats.

For much of this election cycle, Democrats complained the polls were biased against them. They said the polls were failing to represent enough minority voters and applying overly restrictive likely-voter screens. They claimed early-voting data was proving the polls wrong. They cited the fact that polls were biased against Democrats in 2012.

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The Democrats’ complaints may have been more sophisticated-seeming than the ”skewed polls” arguments made by Republicans in 2012. But in the end, they were just as wrong. The polls did have a strong bias this year — but it was toward Democrats and not against them.

The overall result of a D +4 bias in Senate races and D +3.4 in statehouse races in polls within the last 21 days of the campaign masks the true state of affairs. For instance,

It is difficult, if not impossible, to explain any of these results without using the word “bad guess” at some point. In governor’s races, the polls missed Maryland’s results by nearly 12 points and Kasich’s romp in Ohio by 10.

In the aftermath, pollsters closed ranks and many asserted that the internal campaign polls were very close:

Contrary to the many public opinion polls that showed Democrats and Republicans deadlocked heading into Election Day, most …read more    

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