PIck a number, any number

Ever notice that many pill prescriptions last seven days? Why?

Daniel Gilbert, a professor of psychology at Harvard, writes that certain numbers have magical properties.

The magic numbers are the familiar ones that have something to do with the way we keep track of time (7, say, and 24) or something to do with the way we count (namely, on 10 fingers). The “time numbers” and the “10 numbers” hold remarkable sway over our lives. We think in these numbers (if you ask people to produce a random number between one and a hundred, their guesses will cluster around the handful that end in zero or five) and we talk in these numbers (we say we will be there in five or 10 minutes, not six or 11).

Important decisions are made on the basis of magic numbers.

A recent study of antibiotic treatment published in a leading medical journal began by noting that “the usual treatment recommendation of 7 to 10 days for uncomplicated pneumonia is not based on scientific evidence” and went on to show that an abbreviated course of three days was every bit as effective as the usual course of eight. My doctor had recommended seven. Where in the world had seven come from?

Italy! Seven is a magic number because only it can make a week, and it was given this particular power in 321 A.D. by the Roman emperor Constantine, who officially reduced the week from eight days to seven. The problem isn’t that Constantine’s week was arbitrary — units of time are often arbitrary, which is why the Soviets adopted the five-day week before they adopted the six-day week, and the French adopted the 10-day week before they adopted the 60-day vacation.

So if you're told to take three pills a day for seven days, that's 21. But what if your body really only needs 20?

If even one of those pills is unnecessary — that is, if people who take 20 pills get just as healthy just as fast as people who take 21 — then millions of people are taking at least 5 percent more medication than they actually need. This overdose contributes not only to the punishing costs of health care, but also to the evolution of the antibiotic-resistant strains of “superbugs” that may someday decimate our species. All of which seems like a rather high price to pay for fealty to ancient Rome. 

Might be fun to annoy your doctor with this information next time you're in to get some pills.