Saturday, June 02, 2007

(apple+orange)/2 = grapes!

Preemptive warning, in case any readers out there are tempted down the Path of Sin by the comrades at Real Clear Politics. What's wrong with this picture?

Exactly. The top line, or "RCP average." Quick, what's the average of 34% (among 600 likely voters), 27% (among 500 registered voters), and 29% (among some unspecified number of registered voters)? Hint: You can throw in 41% (among who knows how many of what) and toss in 31% (among 801 likely voters) for good measure and you still won't get "30.0."

Well, that's not entirely fair. You can call it "30.0%" all you want. But you might as well call it the Loch Ness Monster, the wreck of the Edmund Fitzgerald or the piece of cod which passeth all understanding, all of which bear the exact same resemblance to the original data as the alleged result presented as the RCP average.

The average of apple and orange is not "grapes." You can't get an average of unlike things. If someone tries to smuggle this bit of nonsense past the vigilant checkpoint that is your copydesk, take it out and shoot it.


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