Thursday, November 04, 2010

Rasmussen Polls Were Biased and Inaccurate; Quinnipiac, SurveyUSA Performed Strongly


Every election cycle has its winners and losers: not just the among the candidates, but also the pollsters.

On Tuesday, polls conducted by the firm Rasmussen Reports — which released more than 100 surveys in the final three weeks of the campaign, including some commissioned under a subsidiary on behalf of Fox News — badly missed the margin in many states, and also exhibited a considerable bias toward Republican candidates.

Other polling firms, like SurveyUSA and Quinnipiac Univesrity, produced more reliable results in Senate and gubernatorial races. A firm that conducts surveys by Internet, YouGov, also performed relatively well.

What follows is a preliminary analysis of polls released to the public in the final 21 days of the campaign. Our process here is quite simple: we’ve taken all such polls in our database, and assessed how accurate they were, on average, in predicting the margin separating the two leading candidates in each race. For instance, a poll that had the Democrat winning by 2 percentage points in a race where the Republican actually won by 4 would have an error of 6 points.

We’ve also assessed whether a company’s polls consistently missed in either a Democratic or Republican direction — that is, whether they were biased. The hypothetical poll I just described would have had a 6 point Democratic bias, for instance.

The analysis covers all polls issued by firms in the final three weeks of the campaign, even if a company surveyed a particular state multiple times. In our view, this provides for a more comprehensive analysis than focusing solely on a firm’s final poll in each state, since polling has a tendency to converge in the final days of the campaign, perhaps because some firms fear that their results are an outlier and adjust them accordingly................................

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