With the Iowa and New Hampshire GOP presidential contests around the corner, and a general election taking shape soon thereafter, you, the politically interested reader, are likely to find yourself swimming in polls.
Polls are very easy to misread, and the media constantly misuses polls. I think most people misunderstand polls.
Here’s one basic thing to note: If you see that one candidate got 10% of a poll of 500 voters, that doesn’t necessarily mean that 50 people said they would vote for that guy. Pollsters adjust their raw data — not in order to tilt the results, but in an effort to more accurately reflect what they think the electorate really looks like.
Maybe by the time the pollster reached 500 likely voters responding (and who’s a “likely voter” is a tricky thing to figure out, and different pollsters have different metrics), they look at their sample and conclude it’s skewed towards rural voters, or females, or people with landlines, or Asians. So they multiply the male or urban voters by 1.15 or something, and multiply the woman and rural votes by 0.92 or something.
Once you realize this, you realize how much of an art is involved in the “science” of polling. So any one poll can only give you a snap shot in time of what the electorate feels, with each pollster injecting his educated guess of what shape the electorate actually takes.
So, some practical advice:
1) Never put too much weight on any one poll. If the latest poll tells you something different from the previous ones, wait to see if the latest poll is an aberration, or the beginning of a trend.
2) Compare any new poll against previous polls by the same pollster to get a notion of trends. That’s what Byron York does in his blogpost on Gingrich’s drop. Comparing a Rasmussen poll today to a University of Iowa poll last week might tell you more about the different pollsters’ methodology than it tells you about trends in public support.
3) Don’t pay attention to polls that are of “adults” or “registered voters.” Only “likely voter” polls are apt to be very meaningful. And in Iowa and New Hampshire, the sample should be at least 500 likely voters.
4) Most polls have a margin of error, and most of those margins ar somewhere between 2 or 5 points. A 2.5% margin of error, for instance, usually means that the pollster is 95% certain that if they had polled the entire population in question, no candidate’s numbers would move up or down more than 2.5%.
As a related point, if Romney is leading Gingrich by 1 point, it’s probably more accurate to say that “Romney and Gingrich are within the margin of error” than to say that Romney is leading.
5) Finally, remember polls can’t directly measure enthusiasm or softness. And they’re often simply wrong.
So, here’s the general gist: use polls of gauges of trends and ballpark figures. Don’t ever use a single poll as a real prediction of election results. That’s one reason I love RealClearPolitics, which aggregates polls, so you can see a bigger picture.
My thinking on polls really benefitted from reading Mobocracy by Matt Robinson.
