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Model Now Has Whitman as Big Underdog in California

While there was an interesting set of polls in Senate and U.S. House races today, the polling load was lighter in gubernatorial contests, with most surveys confirming current assumptions about the races.

That’s bad news for California’s Meg Whitman, the Republican who appears increasingly likely to lose a once-tight race against Jerry Brown. Indeed, that assumption will become more entrenched after three new polls today.

The surveys, from Suffolk University, Fox News, and Public Policy Polling, gave Mr. Brown leads of 8, 9 and 11 points, respectively. While this is the first time that Suffolk has polled California, the Fox News and Public Policy Polling surveys show Mr. Brown having expanded his lead by several points, as other recent surveys have also shown.

As a result of these polls, our forecasting model now gives Ms. Whitman just a 6 percent chance of winning, down from 10 percent yesterday.

At this point — especially with Mr. Brown having at least 50 percent of the vote in several of the surveys — Ms. Whitman’s chances probably rely on there being systematic errors in the polling, rather than her being able to do anything in particular in her last week on the campaign trail to narrow her deficit.

There’s an argument, however — which also has implications for Carly Fiorina, the Republican Senate candidate — that some of the polls suggest a heavier Democratic turnout than it is realistic to expect in this political environment.

For instance, based on an analysis by Real Clear Politics’ Sean Trende, the partisan split in current California polls ranges from 6 to 14 points, favoring Democrats — while the average split is 11 points. By contrast, Democratic turnout outpaced Republican turnout by 12 percent in an exit survey of 2008 general election voters. The argument is that it may be wrong for the Democratic turnout advantage to have decreased by only one point (from 12 points to 11) from 2008 when it will probably be down by more than that elsewhere in the country because of the Republican enthusiasm advantage.

I have addressed a version of this argument before and I do not find it that convincing.

Indeed, I would expect Republicans to narrow the 7-point partisan disadvantage they endured nationwide in 2008 — perhaps to about even. But, this is almost certain to vary from region to region. There are several reasons to think the shift could be less (or there could even be a shift toward Democrats) in California:

  • There is an initiative to legalize marijuana on the state’s ballot, which could draw younger and more liberal-leaning voters to the polls;
  • It is easy to vote by mail in California, which increases the convenience factor and usually results in higher turnout;
  • There has been a long-term trend away from Republican identification in California because of demographic changes in the state’s electorate. Party registration figures show that both Republicans and Democrats have fewer registered voters in the state than they did in 2008, but Republicans have endured a slightly steeper decline (whereas Democratic party registration is off slightly more nationwide);
  • The gubernatorial and Senate candidates in California have spent in excess of $200 million on advertising and voter turnout efforts;
  • There could be regional factors in play, as Democratic polling numbers have also held up relatively well in Washington and Oregon, two other Western states.

But say that you still find implausible a shift from a 12-point Democratic turnout advantage to an 11-point turnout advantage (still a shift in the Republican direction!) The other problem is that it’s not at all certain that the Democratic turnout advantage was in fact 12 points in 2008; it could have been larger (or smaller).

The 12-point estimate is based on an exit poll. This exit poll had a large sample size — about 2,300 people — but it is still just a poll, and subject to various errors. For instance, there are a relatively large number of non-English speaking voters in California, who may sometimes elude pollsters, and who tend to have a Democratic affiliation. And exit pollsters, because they station themselves only at some fraction of a state’s many polling places, use cluster sampling techniques — which can introduce error even when the sample sizes are large. People sometimes treat exit polling data as though it’s ‘hard’ evidence, but it’s not immune from the uncertainties intrinsic to all forms of polling.

At some point, if all the other polls are showing a different demographic or partisan split than the exit polls, it becomes likely that the exit poll, and not the other surveys, is the outlier. Also, these comparisons are not always apples-to-apples in the first place, because pollsters have many different ways of asking about a voter’s partisan registration or identification.

Can there be errors in polling? Yes, of course. And as often as not, when the polling is in error, most or all of the surveys miss in the same direction.

But our model accounts for the fact that there can be these sorts of errors in polling: that’s essentially where Ms. Whitman’s 6 percent chances, and Ms. Fiorina’s 8 percent chances, stem from.

About 8,500 people were interviewed in polls of California within the past two weeks. The margin of sampling error on an 8,500-person sample is only about 1 point.

Our model, however, assumes that the true margin of error of our polling average is quite a bit higher than this — about 5 points. Why? Because sampling error (the error that stems from the fact that you’re only picking a randomly-selected subset of the whole population to interview) is just one way that pollsters can make mistakes. Error can also result from difficulties in drawing a truly random sample, from faulty assumptions in your turnout model, from excessive demographic weighting, from last-minute changes in voter preferences, and from other factors.

Perhaps these other types of errors in the suveys are causing against Ms. Fiorina and Ms. Whitman in California. For this reason, we can’t conclude that the Democratic candidates are totally safe.

But we can conclude that they’re pretty safe: that the pollsters would have to have an unusually bad night to get the winner wrong — especially in the case of Ms. Whitman, who is about 7.5 points behind Mr. Brown in the polling average.

I don’t think the argument about the partisan splits in the California polls is persuasive enough to suggest that there is an especially large chance of mistakes in the California polling. I can also think of arguments one could make that the California polls are especially unlikely to show such a large error — for instance, because much of the voting there has already taken place (by mail), and because the polling is quite consistent there on balance, as compared with other states. I don’t know that those arguments are terribly persuasive either. But if you held a gun to my head and forced me to take the long side of the odds that my model is offering in a few states, Ms. Whitman’s race would not be one of the ones I’d pick. Ms. Firoina’s might be a closer call, because of the unusually large amount of resources that national Republican committees are putting into the state at this late hour on her behalf.

But the fact is that California is a really tough state for Republicans, and these two races are likely to be blemishes on what is otherwise a really fine night for them.

Nate Silver founded and was the editor in chief of FiveThirtyEight.