Why do the results of the national opinion polls on presidential candidate preference differ from the results of the state-by-state polls? That’s the question Sean Trende addresses in a recent RCP post which I commend to your attention. The national polls indicate a slight advantage for Romney in the popular vote while the state-by-state polls indicate a slight but statistically significant advantage for Obama.
Using a variety of approaches Mr. Trende attempts to square the circle. Here’s his conclusion:
How do we resolve this? Which will be correct? My best answer is “I don’t know; it is a source of uncertainty in projecting the election.” I suspect one group of polls will converge upon the other in the next week, and we’ll get a better idea.
Historically, the national polls have actually been more accurate than the state-by-state polls. Next Tuesday we may know.
My guess at this point is that Romney will win the popular vote while Obama takes the electoral vote and, consequently, is re-elected. But it’s no more than a guess. It’s just too close to call. I just don’t believe the folks who are predicting a Romney landslide or an Obama electoral landslide and there are both.
There are several problems with that prediction. Among them are that no president has ever won re-election with the economic trends—not just the raw statistics but the trends—as weak as they are now. Presidents re-elected with high unemployment rates had unemployment rates that were notably trending in the right direction. Another is that there is a general tendency for presidents to be re-elected with larger numbers of electoral votes than they had the last time around. If they get smaller number of electoral votes than they did when first elected, they tend to be defeated.