How many times does PPP have to prove itself for some people to stop questioning its results?
Stop questioning their results? Isn't that kind of like saying "just blindly believe"? When is that healthy to do to any polling firm? But since you asked, this is why I question PPPs results: http://fivethirtyeight.blogs.nytimes.com/2012/06/22/calculating-house-effects-of-polling-firms/
Note that this article is from June 2012, just a few weeks ago, thus much more recent than Nate Silver's July 2010 and November 2010 rankings.
But house effects are not necessarily bad things? PPP having a Democratic house effect (which is just the firm's lean in comparison to the collective polling average) works to its benefit when the polls skew too Republican--Nevada/Colorado/Illinois 2010 races, etc. In most of the competitive statewide races in 2010 the Republican lead was overstated. I don't see why this would necessarily be much different in 2012, considering PPP's solid track record especially when compared to the highly schizophrenic Rasmussen results, but we shall see.
This is from the actual article I posted: The philosophy of the model is simply to strip most of the house effect out of the poll. So a Public Policy Polling survey that showed Barack Obama ahead by seven points in Colorado would be treated as more like a four point lead for Mr. Obama once its house effect is accounted for.
How is that not directly applicable here?
That's only confirming that according to polling averages, PPP skews Democratic so the model treats it as such. But polling averages can be wrong, and in the most recent swing polling of 2010/2008--the polling averages often tilted too Republican and lowballed Democratic numbers.
