I’m not a statistician, or even a math student. But a number of people seem to not know how to read polls, or how to understand them. Some of this is due to a lack of understanding about methodology–some of it due to paying more attention to the headlines than the polling data itself. So here is a friendly guide.
First: a poll usually contains somewhere between 1000 and 3000 respondents, randomly selected so they can get a representative sample. Pollsters work very hard to try to remove any sort of systemic bias, both from their methodology and their results. For politics, they will often assign a party weighting system–that is, if more Americans identify as liberal than conservative, they will weight the results so it gives a reflection of that.
I don’t know the actual details behind this–that is what the pollsters are for. But let’s look at what I do know.
- 1000-3000 is not the entirety of the American population. There will be errors. Some places have a house effect towards one candidate–this is not because the pollsters are biased, it is because their methodology isn’t working.
- Nevertheless, the results are remarkably stable and show clear trending over the course of an election. The pollsters are evidently doing something right.
- This is true despite the fact you occasionally end up with an outlier.
But let’s look more into how to read the polls. It is generally not the best idea to simply pick a pollster and rely exclusively on that one. So the first step in reading the polls is to read a number of them. Gallup is good, Rasmussen is good, they are both showing different numbers. Instead of assuming one of them is wrong and the other is right, perhaps you should consider taking them both into consideration? The more data, the better. If there is a legitimate trend, it will be reflected in multiple polls. CNN even conducts a “poll of polls” to get a better idea of the overall mood. And of course, fivethirtyeight.com, pollster.com, and realclearpolitics.com also perform poll aggregations (and include state polls).
But it’s also really tempting to assume, based on a poll’s numbers, that it is because of something your beloved candidate did or didn’t do. Guessing the motivations of the American public is tricky at best, so I recommend against this, but if you really want to see why there’s a change, look at some of the other numbers, and compare them to what they were earlier. Many pollsters report on a number of factors. They might ask if you feel confident or content that the economy will get back on the right track if this candidate wins. They might ask if you feel he is knowledgeable, or ready to lead, or understands your needs. They might ask if you feel confident that if he is elected the nation will have a good, capable leader.
These numbers are not reflected in the topline “Obama is up by eight points” data–but it can give you a good indication of a number of things. Are the people afraid of Obama? Is he likely to lose supporters? Is McCain’s negative campaigning having the desired effect? Is the race tightening because of that? Is the candidate improving his positive view among the American public, or are they increasingly worried about him?
These numbers make up the difference between a hesitant “I support John McCain” and an enthusiastic “I support John McCain.” You have been seeing the race tighten in the past few days, but the public doesn’t seem more optimistic about John McCain as president. I suspect what you’re seeing is a number of undecideds seeing that McCain is about to lose and deciding they are going to support him. They just aren’t happy about it.
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