Wednesday, March 09, 2011

On That PPP Poll....

You remember that PPP release which told us that "Barrett would win the election if it were held today"? Came out about a week ago.

LegalInsurrection polled (cough) a Ph.D. candidate in polling...

Say someone wishes to know how many people abandoned Walker in hindsight for Barrett, and wants to adjust for this oversampling. This makes sense because the poll asks who previously voted for Walker, so we can compare changes within the same group. This means that the slight difference in voter composition is unlikely to matter, since we are comparing the same people. It is unlikely that a slightly different voter composition would have a significantly different amount of change. In the PPP poll, the group sampled went from claiming they voted 47-47 to giving Barrett a 45-52 advantage, creating a 7 point deficit for Walker

Long story short: the poll is extremely unreliable.

...From what we know, despite the somewhat unrepresentative sample, it looks like Walker has probably lost a bit of support between November and the PPP poll, since even ridiculously optimistic assumptions only account for half of his losses. Is it possible that even after adjusting for union support and people lying about for whom they voted, there is some other factor that contributed to the retrospective tie that can explain away Walker’s losses? In theory, yes, but it is extremely unlikely. Is it possible that this is due to sampling error? Yes, but again, the difference is large enough that that is also unlikely. Hopefully I have shown how little an impact small differences tend to have on final numbers.

For you math geeks, go to the link.

1 comment:

Matthew Knee said...

Sorry, but alas you misread me. I was showing that the bias in the sample could not account for Walker's losses. Even using an absurd set of assumptions to maximize possible impact, I could only chalk up half of Walker's losses to bias, meaning that a lot more than half of his losses are likely real. My conclusion is that Walker did in fact lose some ground.