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Full Moon Effect On Behavior Minimal, Studies Say

John Roach
for National Geographic News
Updated February 6, 2004
 
Beware: The moon is full tonight. People will party. Dogs will bite. Robbers will steal. Murderers will kill.

Contrary to popular belief, however, the frequency of these behaviors will probably be no more significant tonight than on any other night of the year, according to scientific reviews of the theory that the full moon alters the way humans and wildlife behave.


"My own opinion is that the case for full moon effects has not been made," said Ivan Kelly, a Canadian psychologist at the University of Saskatchewan in Saskatoon, Saskatchewan.

Kelly has published 15 papers on the topic and reviewed more than 50 others, including one that covered some 200 studies. He concludes that there is not strong evidence of an effect.

"The studies are not consistent," he said. "For every positive study, there is a negative study."

Loony Dogs?

Case in point: Two separate studies published in the December 23, 2000 issue of the British Medical Journal contradict each other on the question of whether animals bite people more during a full moon.

Chanchall Bhattacharjee and colleagues at the Bradford Royal Infirmary in Bradford, England, reviewed 1,621 patients admitted to the infirmary's emergency room between 1997 and 1999 for animal bites and found that the chances of being bitten were twice as high on or around full-moon days.

But Simon Chapman at the University of Sydney in Australia compared dates of admission for dog bites to public hospitals in Australia with dates of the full moon over a 12-month period and found no positive relation between the full moon and dog bites.

In fact, Chapman found that full-moon days were associated with slightly lower admissions—4.6 compared with 4.8 per day. Of the 18 days with more than 10 admissions, the maximum peak centered on the New Year holiday. Full moons coincided with none of the peaks.

Chapman, who said the study was a "one-off curiosity driven exercise," has no idea why the full moon appears to cause animals in England to bite more humans but has no bearing on when dogs in Australia bite.

Similar contradictions can be found when comparing many other studies as well, such as whether or not violence, police arrests, or self poisoning increase during a full moon, according to Eric Chudler, a psychologist at the University of Washington in Seattle.

"Of the studies I have read, I find that there is very little evidence that the full moon has a direct effect on human or animal behavior," he said.

Selective Memory

Regardless of what the studies say, the power of the moon is often used to explain a wide range of events, from human insanity, violent crimes, and traffic accidents to putting people in a celebratory and romantic mood.

Why? "One reason is that people have selective memories," said Chudler. "When something unusual happens and there is a full moon, people might notice the moon and assign blame."

Another mistake, according to Chudler, is failing to make the distinction between correlation and causation. He notes that just because a study finds a relationship between a full moon and certain behavior, it does not mean the moon caused this behavior.

"These are correlational studies," he said.

Kelly suggested that people who conduct studies on the relationship between the full moon and human behavior often do not collect data throughout the entire month to see if the behavior is more elevated at full-moon time compared to the rest of the month.

Another problem, suggests Kelly, lies in media coverage.

"Journalists pay too much attention to finding sensational news or news that will support interesting results," he said. "Hence [they] ignore the findings of studies and tend to prefer stories or anecdotes from policemen or nurses."

Or studies purportedly backed by a tequila manufacturer.

According to a report in the British newspaper The Daily Telegraph Mexican tequila distiller Jose Cuervo sponsored a psychiatrist at Kings College in London to study the association between the full moon and strange behavior as portrayed in literature.

The psychiatrist, Glenn Wilson, found that the full moon has been portrayed in folklore and legends for centuries as cause for celebration, particularly in the times before modern lighting.

"There is good reason to believe that people's personalities do change around the time of the full moon, not because of any astronomical force, but because it creates the optimum lighting conditions for feeling carefree and mischievous," Wilson told the paper.
 

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