Silver weighs in on pollster controversy

Yesterday, I wrote about the spat between Democracy Corps’ Stan Greenberg and Resurgent Republic’s Ed Gillespie. Long story short, Greenberg had some beef with Gillespie’s recent poll results. Specifically, he called out RR’s finding that Democrats had only a +2 percentage party ID advantage. (If you don’t include “leaners,” the spread is about +4).

Today, Nate Silver has a fairly exhaustive post on the dust-up. Silver finds that the average party ID advantage for Democrats in other polls is +9.8. His conclusion:

So let’s evaluate a 4-point partisan ID advantage for the Democrats: is it proper to term this an “outlier”, as Greenberg does?

[snip…lots of statistical stuff….graphs…]

If we assume that the 9.8-point value is the “true” and correct result, then a 4.5 point advantage would not be all that out of line…..if we assume that the “true” distribution of registered voters in the population is, say, 37.4 percent Democrat, 27.6 percent Republican and 35.0 percent independent (giving the Dems a 9.8-point advantage), the odds of the Democrats winding up with no more than a 4.5-point advantage in a 1,000-person sample is about 2 percent due to chance alone–somewhat unlikely, but far from impossible. Moreover, since we do not have any a priori way of knowing the “true” number of registered Democrats and registered Republicans (many states either do not report registration figures, or do not require voters to register by party at all), it becomes harder still to characterize Resurgent Republic’s results as an outlier.

What we can say, however, is that if Resurgent Republic consistently shows a smaller partisan ID gap than other pollsters, it will become progressively harder–and will eventually become entirely impossible — to attribute these results to chance alone.

So. Thus far, there’s no evidence to attack RR’s methodology. If they continually find results that more favorable to Republicans, something might be up.