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Three Reasons for Surprising Polls

October 27th, 2004, 5:30am by Sam Wang

Hawaii has been added because of two recent polls showing possible leads for Bush. This seems very unlikely. In any event, what is really needed is a third poll.

With that, let’s think about a favorite subject of mine: why individual polls seem surprising or contradictory. I can think of three reasons:

1. Reporters often don’t understand statistics. A poll showing Bush up by 5% and another showing Kerry up by 1% are in fact consistent with one another because of random sampling error. For more on this read yesterday’s entry by Mystery Pollster (Mark Blumenthal). A better way to get a good answer is to examine many polls at once. For the record, Charles Forelle at the WSJ is a very notable exception – in his article about this Web site and others, he captured the subject perfectly!

2. Man bites dog. When a poll’s finding sounds interesting, it gets more attention than a boring result. Therefore reports of outliers tend to grab headlines, creating apparent discrepancies.

3. Competition among organizations. News organizations usually rely on their own data alone. If they do this, they cannot achieve the increased accuracy that comes from comparing multiple polls. Indeed, little incentive exists to improve accuracy, since low accuracy leads to more frequent news stories, and therefore more readers or viewers.

Tags: 2004 Election

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