There will be a serious, critical look at the final pre-election polls in the Democratic presidential primary in New Hampshire; that is essential. It is simply unprecedented for so many polls to have been so wrong. We need to know why.

But we need to know it through careful, empirically based analysis. There will be a lot of claims about what happened - about respondents who reputedly lied, about alleged difficulties polling in biracial contests. That may be so. It also may be a smokescreen - a convenient foil for pollsters who'd rather fault their respondents than own up to other possibilities - such as their own failings in sampling and likely voter modeling.

There have been previous races that misstated support for black candidates in biracial races. But most of those were long ago, and there have been plenty of polls in biracial races that were accurate. (For more on past problems with polls in biracial races, see this blog I wrote for Freakonomics last May.) And there was no overstatement of Obama in Iowa polls.

On the other hand, the pre-election polls in the New Hampshire Republican race were accurate. The problem was isolated to the Democratic side - where, it should be noted, we have not just one groundbreaking candidate in Barack Obama, but also another, in Hillary Clinton.

Full article here.