Monday, July 12, 2010
Rasmussen's Senate House Effect
But does Rasmussen have a large pro-Republican house effect in 2010? Looking at the generic ballot, the answer seems to be absolutely. Using only Rasmussen polling, the Pollster.com aggregate gives the House Republicans a 7.3% advantage as of this writing. Using all other pollsters except for Rasmussen, House Republicans hold only a 0.1% lead. Some of this may be their use of a likely voter model, although it is unlikely that it accounts for all of Rasmussen's difference.
Of course, the generic ballot is only one of the many contests that Rasmussen polls. Rasmussen has accounted for a little over 50% of the legitimate polls conducted for United States Senate races in 2010. Being that Rasmussen has flooded the zone, we must ask whether their Senate polls have had the same sort of bias as their generic ballot. Many liberals would like to believe so, but no one to my knowledge has affirmed or disproved it... until now.
David Shor, a visiting graduate student collaborator at Princeton University, has estimated Rasmussen's house effects in all possible Senate races (his methods are outlined here). Using data supplied and collected by Rasmus Pianowski and me, he found that the difference in house effects between Senate races to be mostly insignificant (or "eerily consistent") . However, the difference between Senate races and the generic ballot was highly significant.
Does this variation in generic vs. Senate house effects make a difference in terms of how many seats Republicans would pickup if the election were held today? Shor, who, along with his Stochastic Democracy blog team, Princeton Election Consortium, and me launched a preliminary 2010 Election Projection System, has shown that differing house effects do make a difference in our projections. Instead of the Republicans picking up 3 seats, they are predicted to pick up 5 seats with Missouri and Pennsylvania falling into the Republican column.
It should be pointed out that Rasmussen, like any other pollster, will have outlier polls that will not fit perfectly in with any assigned house effect. Still, when viewing Rasmussen's Senate polls, one should realize that these polls tend to be more pro-Republican than other polls, but not as pro-Republican as Rasmussen's generic ballot polls.
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