Some Likely Voter Models are Suspect

[Secret_Society]

There are eight current national polls that list separate sets of results for likely and registered voters. (In this case, for reasons that will be apparent momentarily, I am deliberately double-counting the two Gallup likely voter models). On average, Barack Obama leads by 9.8 points in the registered voter versions of these polls, but by 7.0 points in the likely voter versions -- nearly a 3-point difference:

<http://www.fivethirtyeight.com/>

Note, however, that the likely voter models appear to segregate themselves into two clusters. In one cluster, there is a rather large, 4-6 point difference between registered and likely voter results. In the other cluster, there is essentially no difference.

The first cluster coincides with Gallup's so-called "traditional" likely voter model, which considers both a voter's stated intention and his past voting behavior. The second cluster coincides with their "expanded" likely voter model, which considers solely the voter's stated intentions. Note the philosophical difference between the two: in the "traditional" model, a voter can tell you that he's registered, tell you that he's certain to vote, tell you that he's very engaged by the election, tell you that he knows where his polling place is, etc., and still be excluded from the model if he hasn't voted in the past. The pollster, in other words, is making a determination as to how the voter will behave. In the "expanded" model, the pollster lets the voter speak for himself.

Frankly, I find polls showing a 4-6 point gap between likely and registered voters to be utterly ridiculous. Why?


(Go to fivethirtyeight.com for the full analysis)


I would like to issue a challenge to those pollsters like Franklin & Marshall and GfK which in spite of all the facts above, are showing a substantial shift toward the Republicans when they apply their likely voter models. E-mail me -- my contact information is at the top of the page -- and tell me why you think what you're doing is good science.

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Let's not worry too much about that AP poll