Commentary By Ron Beasley
Electoral-Vote.com was one of the more reliable sources for election prediction in 2008. They have this to say about Rasmussen:
After the 2010 elections, the New York Times statistics wizard, Nate Silver, analyzed the polls produced by various polling organizations, including Rasmussen Reports, which is the house pollster for Fox News. Silver's analysis covered only polls taken during the final three weeks of the campaign and compared them to the actual election results. For polls taken much earlier, say in June, no one knows what the true sentiment of the electorate was, so there is no way to tell if the polls were accurate or not. Also, any pollster deliberately falsifying the results for partisan advantage would be advised to reduce the bias as the election neared. After all, no one can tell if a June poll is accurate but everyone can tell if a poll released the day before the election is accurate.
Silver analyzed 105 polls released by Rasmussen Reports and its subsidiary, Pulse Opinion Research, for Senate and gubernatorial races in numerous states across the country. The bottom line is that on average, Rasmussen's polls were off by 5.8% with a bias of 3.9% in favor of the Republican candidates.
There is much to criticize about Rasmussen's methods. All polls are conducted within a 4-hour window, the person who answers the phone (even a child) is sampled, phones that are not answered are not called back, and much more. All of Rasmussen's polls are done by computer; live interviewers are never used. However, other firms that do robopolling such as SurveyUSA and PPP get much more accurate results with no bias, so the problem is not the robopolling per se.
Just to look at one methodological issue, if no one answers the phone, Rasmussen picks a different random phone number instead of calling back two, three, four or more times as other pollsters do. Why does this matter? Because 20-somethings (who skew Democratic) are often out, whereas 60-somethings (who skew Republican) are often in. By not being persistent in finally getting through to a randomly chosen phone number, the sample is inherently biased towards Republicans because they are easier to reach. This may not have been intentional but it is understandable if you want to finish your survey in 4 hours. Nevertheless, cutting corners in the name of speed and cost don't improve accuracy.
They give their projections both with and without Rasmussen. When looking at the electoral college vote there is some but not a lot of difference. But when you look at Senate races there is.
The projections with Rasmussen is Democrats 50, ties 3 and Republicans 47.
This is the Senate map without Rasmussen - Democrats 52, tie 4 and Republicans 44.
Montana and North Dakota actually flip and Virginia goes from Republican to tie.