The Rasmussen Secret Sauce: Pennsylvania Governor Edition

Are we tired of Pennsylvania yet? Of course not! Specifically we now check in on the Governor’s race. Rasmussen has released the first poll since the primary, but I will compare that with the last pre-primary Quinnipiac poll anyway. Tom Corbett and Dan Onorato were obvious likely nominees.

I believe we have as much to learn about Rasmussen’s distinctive modeling as we do about the race itself.

Both polls have Republican Corbett ahead, but the post-primary Rasmussen poll gives him a much larger lead over Democrat Onorato than the pre-primary Quinnipiac poll. Rasmussen shows Corbett 49, Onorato 36 (MoE 4.5) for a whopping 92% lead probability, while Quinnipiac has the race a bit closer at Corbett 43, Onorato 37 (MoE 2.9) and an 84% lead probability.

Both polls look very good for the Republican at this point, and show Onorato as being in need of a post-primary unity bounce as passions cool after the multi-way primary. But why does Rasmussen show so many more Republican supporters?

I think the key is that Quinnipiac has no secret sauce, and merely polls Registered Voters, while Rasmussen has his “House Effect,” as Nate Silver calls it, of likely voter filtering. He’s just assuming Republicans and right-leaning Tea Party voters will have more enthusiasm to vote this year, and that should be making his polls favor the Republican.

Quinnipiac gives Onorato a 34-13 favorability margin, and Corbett 49-13. Rasmussen shows 46-32 and 57-26 if we add strong and weak readings, or 15-14 and 27-11 if we only include the strong feelings. In other words, Onorato’s favorability ratings simply collapse in Rasmussen versus Quinnipiac.

Rasmussen’s final polls for the Democrats in their primaries for Senate and Governor were closer than both of Quinnipiac’s last readings, but I’m not sure how relevant that is to this issue. In theory Rasmussen could be the most accurate pollster on earth, but be entirely wrong in the profile of a likely voter in November 2010.

I have to think this election will bolster or destroy Rasmussen’s credibility as a public political pollster. The firm is going way, way out on a limb, and if it breaks, the wolves below are ready to kill. There’s no middle way here. You can’t substitute your own judgment for the 2006 and 2008 electoral history, and walk away unscathed if you’re wrong.