Last week, a CBS News / New York Times Poll showed that the Democratic race for the presidential nomination may be tightening. It had Hillary Clinton with only a 7 point lead over Bernie Sanders -- far closer than other polls have shown.
But that poll could be an outlier, because two new polls show Clinton with a much larger lead nationally. Both of them have Clinton with a 25 point lead nationally over Bernie Sanders.
The first is the NBC News / Wall Street Journal Poll -- done between January 9th and 13th of a random national sample of 400 Democratic primary voters, with a margin of error of 4.9 points.
The second is the latest YouGov Poll -- done between January 9th and 11th of a random national sample of 620 Democratic primary voters, with a margin of error of 4.2 points.
Never trust a single poll. I love statistics. Most of my post-doc work dealt with Monte Carlo simulations, so statistics is kind of my thing. And the general level of ignorance about statistics is stunning. I commonly hear it said, "These two numbers are within the margin of error, so they are tied." No! It doesn't mean that any more than a difference outside the margin of error means that one person is winning. It's all about probabilities. If one person is winning by one sigma, there is a 66% chance they are actually winning. (Assuming the polling sample is not skewed.) If they are winning by three sigma, there is a 99.7% chance they are winning. (These are just what I recall, I haven't looked them up recently; don't quote me.) The human brain did not evolve to deal with this kind of stuff. And that's fine if it were limited to pointy headed academics. But when it's presented on the TV news, it's a mess. The big problem is that there are so many polls. If you poll something long enough, you will get wildly incorrect answers from time to time, even though the polls are perfectly fine.
ReplyDeleteSorry for going on about that. I do love it. Statistics is great fun!
But these polls do show that Sanders is doing better than I had expected when he entered the race. I thought he had a ceiling of 25% at most.
You are absolutely correct about polls. If you poll long enough, you will get an outlier. Polls can also depend on the way a question is asked. And even the best poll is just an educated guess. However, as you can deduce from my blog, I love polls (and also studied statistics in college). I do think you can get a pretty good idea of what's going on when several polls all show the same thing.
ReplyDeleteI agree that Bernie is polling a bit better than I expected -- but I still think Hillary has a fairly comfortable lead nationally, at least for now.
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