November 22, 2006

An Average Weather Report: On the Role of the Media in Science Education

Average Weather      Normal-Weather

The above graphics come from two different weather reports by two different reporters on our local CBS affiliate. I'm not showing these to cause envy among those of you from less temperate climes. I have something else in mind. Ignoring the differences in background and font, two other, more important differences, can be seen. The one on the left uses the degree sign while the one on the right does not; and the one on the left says "average" while the one on the right says "normal." Jackie Johnson, who has a degree from University of Southern Alabama, with a concentration in meteorology, presented the one on the left. The one on the right was presented by Johnny Mountain whose listed qualifications are "weatherman" and who, because of his showmanship, has the most prominent time slots. My favorite KCBS2 weather reporter is Josh Rubinstein, but I couldn't find one of his reports online. Josh uses "average" rather than "normal" and he has some formal training in meteorology.

So what is my point? Average is a well-defined mathematical term. "Normal" in this context is a hyped-up pseudo-synonym for average. The average temperature may or may not be normal. It is at least possible, if very unlikely, that the average temperature never occurs. Presenting the mode for the day might be closer to presenting a "normal" temperature but a range would even be better, say between the one-sigma points. In any case, using the word "normal" to mean "average" teaches bad math and bad science. I also think not using the degree sign is also a bad idea. Sure, we don't commonly use it in popular speech but that is a lazy error not some better way of communicating the temperature. Oh, yes, and I think they need to indicate that this is on the Fahrenheit scale but I would feel much better if Johnnie Mountain would just stop using "normal" when he means average.

Truthfully, this isn't such a big deal. It sure isn't CBS's most grievous failure when it comes to their fiduciary responsibilities to promote good science. Their occasional forays into ghost stories have that category sewn up. I would guess that when it comes to the weather the average for a given day is fairly close enough to "normal" for most practical purposes. The problem is that this error of confusing the average with the normal is presented every day at 6:00 PM. As a society, we have more than enough problems getting our minds around statistics. We don't need one of the common errors reinforced every night on the news.

Posted by DuaneSmith at November 22, 2006 03:19 PM | Read more on Science - General |

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Does the daily temperature variation follow a normal distribution? If not, a range defined by "between the one-sigma points" may not be too meaningful either.

Posted by: Aydin at November 24, 2006 05:07 AM

Damn straight! But even our heros at MythBusters can make a common TV-style error.

Experimenting with a homemade rocket propelled boat, Jamie mused it mighta gone faster it the rocket had been pointed into the water so it woulda had something to push on!

Posted by: Tailspin at November 26, 2006 01:54 PM

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