Illinois State University Department of Mathematics

Here are links to the whole story:

Tuesday 2/18/14: An informative NPR story about our country's less-than-successful transition to CFL and LED light bulbs.

Wednesday 2/19/14: Roger Day offers up story correction to Robert Siegal via email.

Thursday 2/20/14: NPR corrects the light-bulb story. Listen to or read the NPR correction.

I enjoyed and learned from yesterday's (2/18/14) story on the slow and less-than-successful transition to non-incondecsent light bulbs.

At one point in the story, Robert Siegal was introducing an expert who described how life-span estimates are calculated for bulbs. Robert mentioned that a MEAN is computed and then introduced the expert. The expert described the process of obtaining a large number of bulbs, switching them all on, and then measuring time until exactly half the bulbs remained lit (or half had burned out).

This time measure, of course, is the MEDIAN, the physical middle of a data set! A MEAN couldn't have been computed until all bulbs had burned out, because the MEAN requires all values to be known, as we sum the values (burn times, here), and divide by the number of values (here, the total number of bulbs tested).

Thanks for setting the record straight!

Roger Day, Mathematics Department, Illinois State University

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