Thursday, October 23, 2008

Percentage points

In a list of things to be irritated about, the following is probably not at the top of the list, but time is short today, and this topic is somewhat significant. It is the confusion on the parts of many people between "percentage" and "percentage points," one that is typified by this comment (identification withheld because it's just too prevalent to single out one writer):
A poll commissioned by the New York Times and CBS News found that 23 percent more people think McCain is very knowledgeable about foreign affairs compared to Obama – 45 percent to 22 percent.
(This is from a while ago, I think the numbers are different now.)

This statement is simply wrong. It's not that 23 percent more people thought McCain knowledgeable, it's 105 percent - more than twice as many. It's 23 more percentage points, a number far more contextual (99% - 76% gives one a far different perception than 27% - 4%).

I don't think I expect too much of the media that they get things like this right. But their inability to handle simple statistical concepts allows them to be manipulated, witness some of the National Sales Tax movement members. Their marketing concept is that, in charging a 30% sales tax, they can call it 23%. What they do is divide the increase by the result (30/130), an intellectually bankrupt attempt at sugar-coating the bite. And I've read articles which cite a 23% increase, or discuss it as a "point of contention." No, it's a lie, and it comes directly out of an inability or unwillingness to learn junior high-level statistics.

It's hard to see how we can trust members of the press on anything regarding numbers, and a financial crisis brings forth a lot of numbers, when they fall prey to simple mistakes like these.

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