Tuesday, December 20, 2005

Rate vs. Number

A small numerazzy to my morning paper today for this headline over this story (and first two grafs for explanation):

State highway death
rate surpasses 2004's
More people have died on South Carolina roads this year than in 2004, the state Department of Public Safety said Monday.

Through early Monday afternoon, 1,050 people had died on the state's roads, up from 1,046 last year.

The story goes on to talk about the typical number of people who die in December and that 1972 was the record year for highway deaths.

Did you catch the error?

It's the use of rate in the headline. The state's figures are not a rate, just a number. Nowhere in the story is a rate listed. In fact, it's quite possible the rate per, say, miles driven is down, even though the death total or toll is up, especially if somehow the miles driven has increased sharply.

Moral: Don't get the terms confused. A rate requires a denominator, a "per whatever." This headline should have used total or toll to be numerically correct.


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