How much is Rasmussen polling influencing the outlook on the 2010 Senate elections? To find out, I produced updated three forecasts this morning: one without any Rasmussen polls, one with only Rasmussen polls, and one with all polls. Here are the results:
The 22 Senate seats that might switch partisan control
The chart below looks only at current primary campaign leaders. Campaigns where incumbent party currently leads by 18.5% or more are considered "safe," and not listed.
* = In Arizona, I am currently projecting J.D. Hayworth to be the Republican nominee
Here are the projected Democratic seat totals for all three of these forecasts:
At first glance, Rasmussen appears to be weighing down the projection quite a bit. The overall forecast (52.49 Dems) is significantly closer to the Rasmussen-only projection (51.69 Dems) than to the non-Rasmussen projection (54.37 Dems).
- No Rasmussen: 54.37
- Only Rasmussen: 51.69
- All polls: 52.49
For the 19 campaigns where there is a comparative trend, the Rasmussen poll average shows Republicans performing much better than the average of all other polls. The median pro-Republican house effect is 7.0%, and the mean is 6.4%. The difference is by no means consistent, as Rasmussen actually shows Democrats performing better in Pennsylvania and Washington than do other polls, and about the same as other polls in California, Iowa and Illinois. As such, just tacking on 6.4%, or 7.0%, to the Democratic candidate in Rasmussen polls would not likely increase the accuracy of an election forecast.
Personally, I am still going to stick with the average of all polls, for now. In the meantime, I will be conducting some research to see if weighting polls by "house effect" would have produced more accurate forecasting results in the 2004, 2006 and 2008 elections. If it does, then I will start weighting polls by house effects. If it does not, then I won't.