Morning Jay: Are the Polls Tilted Toward Obama?
6:00 AM, Sep 26, 2012 • By JAY COST
If it comes down to whether or not this will be a repeat of 2008 -- which is basically what the latter camp of pollsters is suggesting -- then my money is on no. Of course, it is possible that I am wrong. I have no crystal ball looking forward. All I can do is look back through history, where I see on average a nationwide Democratic identification edge of about 3 points, which is also roughly the midpoint between 2004 and 2008. That is my guess about 2012. It is an informed guess, but it is still a guess. If I’m right, then Rasmussen, Purple Poll, Mason-Dixon, and Survey USA are closer to the mark. But I could be wrong, in which case Fox, PPP andWashington Post are closer to the mark.
Importantly, the pollsters are guessing, too. They are guessing via the myriad of choices they make about when to poll, whom to poll, and how to poll. By Election Day, polling will be much more “scientific” than it is today; but now there is quite a bit of “art.” That's how we wind up with two points of convergence, instead of just one.
Another point to keep in mind: bimodal distributions are extremely messy to deal with. It is hard to average them in a meaningful way, and analysts who build complicated predictive models based on these sorts of polls are going to have a difficult time handling them.
Second major point: There is a subtler dimension to this Democratic polling advantage, one that nevertheless exercises a powerful effect on the margins between the two candidates. And it looks to apply to most of the polls, at least for the time being. It has to do with how tightly the two sides have control over their own coalitions. For instance, a recent Rasmussen poll had Romney winning 85 percent of Republicans, and Obama winning 11 percent. So, we might say that Romney is pulling a net of 74 percent from his own side.
We can replicate this methodology for recent polls that provide enough data.
As we can see, Obama has tighter control over his base at the moment. Now, the difference may seem insubstantial, but I assure you it is not. After all, this is a race that will see the two sides separated at most by 5 points, so this basically gives the president a one-point boost over Romney, simply by virtue of having a more unified base.
But is this historically accurate? Not really. In fact, over the last forty years, Republican candidates have consistently had tighter control over their base than their Democratic counterparts. Here is the most recent historical data from the exit polls:
The GOP control over its base has been remarkably consistent over the last forty years (at least in years without a major third party challenger), falling within a very tight range of +81 and +87, for an average of +84 over the last three cycles. The Democrats, meanwhile, had problems up through the 1980s, as the old New Deal/Great Society coalition was breaking down. Nevertheless, the party has since been rebuilt with a relatively loyal base of support. If we control for the Nader factor in 2000 breaking apart the Democratic base at the margins, then they are probably averaging about 78 or 79 percent these days.
Notice that the GOP outpaces the Democrats in party unity. That was true even in 2008, which was the best year for the Democrats and the worst for the Republicans in a generation. But notice also that the average of recent polls has the Democrats more unified than the GOP. That is a historical anomaly.
Again, it is possible that history will be defied, but I am rarely one to bet on that happening. If we instead assume that the GOP will have a net of +84 among its own partisans, and Obama can recreate the +79 he managed in 2008, then we are talking about a 2-point shift in these polls in favor of Romney. In other words, the above national polls give Obama a 3.6 percent edge over Romney; if the two bases fall back into historical alignment, then that lead would be cut to about 1.5 points.