Nate Cohn

Nate Cohn @Nate_Cohn

That's definitely not the way things work now, if it ever was. Whether due to low response, noncoverage or opt-in sampling, pollsters don't have unbiased samples. Instead, they do a bunch of increasingly heavy handed statistical adjustments to compensate. — PolitiTweet.org

Nate Cohn @Nate_Cohn

These choices sometimes put pollsters at odds with poll aggregators. A poll aggregator prefers an unbiased poll, even if it's noisy. A pollster wants to reduce error, and might make choices that induce bias to poll it off--weighting by party identification, to take an easy one — PolitiTweet.org