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FiveThirtyEight

Politics

We seem to have gotten past some point of no return where we have a half-dozen polls or so to look at almost every day:

A lot of these polls are good news/bad news for both candidates. In Rasmussen’s poll of Mississippi, for instance, Barack Obama hasn’t improved his numbers from the May edition of the poll, which had also showed him trailing by a 50-44 margin. On the other hand, that result had looked to me like an outlier before, and now can probably be taken more credibly. While Mississippi remains a longshot for Obama, keep an eye on Louisiana, which has similar demographics but much bluer party identification figures.

The two polls of Texas show the race tightening, but probably not enough to make the race interesting. There’s a good rundown here of the pros and cons of Obama investing resources in Texas. The only thing I’d add is that there is far more room at the margins for the Democrats to make up ground with registration among Latino voters than among African-Americans. If Tejanos vote in anything resembling the same proportion that they constitute of Texas’s citizenry, the state could be quite competitive.

But it’s the SurveyUSA result in Ohio that I want to focus on. Obama leads by 2 here, but had been ahead by 9 in SurveyUSA’s may poll of the state. That previous poll had shown a heavily Democratic sample — 52 percent Democrat, 28 percent Republican, 18 percent independent — and had triggered a lot of discussion about whether pollsters should be weighting their results by party ID. SurveyUSA does not do so — although if it had applied the May distribution of party IDs to this poll, it would have shown Obama ahead by 10-11 points rather than by 2. Conversely, if SurveyUSA had applied the June party ID distribution to its May poll, that poll would have shown a dead heat rather than Obama ahead by 9.

I do not mean to be a fair-weather fan on the idea of weighting by party ID. As I implied the other day, I suspect that pollsters are facing something of a trade-off between volatility and potentially introducing bias. Weighting by party ID will almost certainly reduce noise, and perhaps make it easier to perceive trendlines — but if the pollster’s guesses about party ID are wrong, they may be reducing the turbulence but landing at the wrong airport. I’ll say this: if a pollster doesn’t know what it’s doing, I think it should be letting the numbers speak for themselves. On the other hand, if the pollster has a robust and thoughtful method for weighting by party ID, it might be worth the trade-off. It is interesting that, taking two of our three highest-rated pollsters, Scott Rasmussen is a firm believer that you ought to weight by party ID, and Jay Leve at SurveyUSA is a firm believer that you ought not.

Finally, there have been some further refinements to the simulation model based on everyone’s feedback, which I’ll get around to explaining in a bit.

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