A couple of months ago, when my fellow surgical residents and I went around a table divvying up nights on emergency room duty, one March date sat conspicuously unpicked--Friday the 13th. C'mon, I thought. This is ridiculous. So when it was my turn again, I put my name down for March 13. Rest up, one resident told me. You'll be in for a long night. I laughed and dismissed the thought.
But looking at my calendar a while later, I noticed that the moon would be full that Friday night. When someone noted that a lunar eclipse would be occurring then, too, I felt my skepticism slip a little. Perhaps I would be in for a miserable night, after all. Trained scientists such as myself, however, do not succumb easily to superstition. Like any self-respecting rationalist, I asked the obvious question: Isn't there a study on this?
It turns out there is one reputable study that has tried to assess whether or not luck actually does go bad on Friday the 13th. (I'm not sure which is more surprising: that someone actually spent time researching this or that I could find only one such study. This is, after all, a world that has studied even how chewing gum distributes saliva around the mouth.) The 1993 study, published in the British Medical Journal, compared hospital admissions for traffic accidents on a Friday the 13th with those on a Friday the 6th in a community outside London. Despite a lower highway traffic volume on the 13th than on the 6th, admissions for traffic accident victims increased 52 percent on the 13th. "Friday the 13th is unlucky for some," the authors concluded. "Staying at home is recommended." How you escape the bad luck at home they didn't explain.
You really can't make much of one study of one Friday the 13th in one town. Lots of other factors could have caused that surge of crashes. Still, Friday the 13th phobia is widespread. Donald Dossey, a North Carolina behavioral scientist, has coined a term for it: "paraskevidekatriaphobia," which he derived from the Greek for fear of Friday the 13th. He estimates that between 17 million and 21 million Americans suffer mild to severe anxiety or change their activities--performing rituals before leaving the house, calling in sick to work, or postponing flights or major purchases--and that businesses lose $750 million in revenues because of these fears.
Superstitions about the moon may be taken even more seriously. For centuries, and in disparate civilizations around the world, people have suspected that the cycles of the moon have a powerful influence over us. A 1995 poll found that 43 percent of people still believed the moon alters individual behavior. And mental health professionals believed it more often than anybody else. The centuries-old word "lunatic" derives from the connection thought to exist between the full moon and madness.
The idea of lunar human cycles seems more plausible than a Friday the 13th effect. Scientists once dismissed daily biological cycles as preposterous, but they now widely accept that body temperature, alertness, memory, and mood all fluctuate according to a predictable "circadian" rhythm. Evidence also shows seasonal effects on mood and behavior.
Ifound some one hundred studies testing for "circalunidian" cycles. My favorite is a five-year study of self-poisoning at a hospital in New South Wales, Australia, published in the Medical Journal of Australia. From 1988 to 1993, the hospital admitted 2,215 patients for overdosing on drugs or poisoning themselves with toxic substances. The researchers checked to see whether peaks in such events occurred not just according to the phase of the moon but also according to one's zodiac sign or numerological readings (as "calculated according to the formulas contained in Zolar's Encyclopedia of Ancient and Forbidden Knowledge"). To no one's surprise, self-poisoning rates were not affected by whether a patient was born a Virgo or a Libra. Nor did Zolar's "Name Number," "Month Number," or "Birth Path Number" for a person make any difference. However, women (but not men) were about 25 percent less likely to overdose around the time of a full moon than around a new moon.
That self-poisonings decrease at the full moon actually correlates with the results of other studies. If any link between psychology and the full moon exists, it seems to be protective. The authors of a 1996 study of 10 years of suicides in Dordogne, France, concluded, in charmingly ungrammatical English, that "the French dies less in Full Moon, and more in New Moon period." Studies in Cuyahoga County, Ohio, and Dade County, Fla., also found a drop in suicides at the full moon. These studies don't quite clinch the full moon's happy effect, however. More than 10 other studies have been done, and they have not confirmed a lunar cycle for suicide.
As for other forms of craziness, the moon seems to have no effect. Researchers have reviewed logs for calls to police stations, consultations to psychiatrists, homicides, emergency room visits, and other measures of our daily burden of madness. They found no consistent relationship, one way or another, with the moon.
Somehow, however, the moon does have an effect on human beings--at least on women. Menstruation typically occurs on the 28 day lunar cycle. And even the phase of the moon matters. In a study of 826 women, 28 percent began menstruating during the four days around the new moon, whereas no more than 13 percent did so during any other four day period. This puts the peak of ovulation at the full moon. (Could this provide an evolutionary explanation for the romantic associations we have with the moon? I'll leave that to Robert Wright, Slate's resident Darwinian, to sort out.) How this happens is baffling. The lone hypothesis I've found proposes that the moon generates tidal forces on the 50 percent to 60 percent of our bodies that is water. But that only raises more questions--such as how tides are supposed to make women menstruate.