For centuries, mankind has been intrigued by the notion that a full moon — which rises tonight — drives people to madness, crime, suicide and major crisis.
It's one of the most enduring myths in human history, embedded in popular culture and folklore from Transylvania and the myth of the werewolf to Creedence Clearwater Revival's breakaway 1969 hit, "Bad Moon Rising." The word "lunacy" has its roots in the Latin word for moon.
And like most popular myths, there's a certain logic to it: Earth is about 80 percent water, much like the human body, the theory goes, and if the moon's gravitational pull can effect the ocean tides, can't it also affect a person's body?
Studies have found that cops and hospital workers are among the strongest believers in the notion that more crime and trauma occur on nights when the moon is full. One 1995 University of New Orleans study found that as many as 81 percent of mental health professionals believe the myth.
But a growing body of evidence in the last 30 years has all but debunked the notion that nothing good can come from a full moon.
"Published [research] does not confirm that there is a change in the amount of violence, reported crimes or aggressive behavior during a full moon," Eric Chudler told ABC News. Chudler, a research associate professor in bioengineering at the University of Washington in Seattle, has studied more than 100 research papers on the purported effects of the full moon on human affairs.
'All Hell Broke Loose'
A touchstone moment for contemporary belief in this myth came in 1978 with the publication of psychiatrist Arnold Lieber's best-seller "Lunar Effects: Biological Tides and Human Emotions," which popularized the gravitational pull theory. In that first edition, Lieber describes how his research led him to fear particularly high levels of trouble during the full moons in January and February of 1974 in Florida, after a study he conducted that purportedly linked the full moon to higher homicide rates in Miami-Dade County, Fla. He writes that he contacted Miami police, media and one hospital administrator to warn them of the expected chaos.
"Sure enough, all hell broke loose," he wrote in a 1996 updated version of the book, retitled, "How the Moon Affects You: A Compelling and Controversial Book on the Awesome Power to Affect Your Emotions and the Way You Live."
What he failed to add was that he'd predicted similar outbreaks of chaos in December 1990 and January 1992, according to a critical review by James Rotton, a Florida psychology professor and well-respected researcher in the field. "Of course these dates passed uneventfully," Rotton writes in "Moonshine," his critical review of Lieber's work for the journal Committee for Skeptical Inquiry.
Another troubling aspect of the book that Rotton challenges cuts to the heart of research supporting the notion of a lunar effect on humans. The original book cites a 1972 study that Lieber and another researcher conducted in which they claim to have found a lunar effect on homicides in Dade County between the years of 1956 and 1970. The book presents a graph that appears to show that homicides in Dade County spiked during full moons, which Lieber wrote that he bases on three studies he conducted that "attained significance," according to Rotton's research.
But Rotton writes that Lieber "neglected to tell readers that [his team] performed 48 tests of significance in all. Not divulging this information is like a gambler failing to tell us how many times a coin was tossed before three heads came up."
Lieber did not return calls for comment from ABC News to his Florida home over the weekend.
The University of Washington's Chudler has been studying the lunar effect phenomenon for years and has concluded that there are a number of reasons why some studies appear to show a connection between full moons and some forms of human madness or calamity. Either the studies tested a few people over a short period of time, didn't analyze their data with proper statistical tests or did not take into account when a full moon occurred on a weekend or holiday — a statistically significant factor in altering people's behavior, he said. Some studies include full moon behaviors that occur a few days before and after a full moon, while others concentrate on only a single day.
Correlation vs. Causation
Chudler explained why it would be virtually impossible to scientifically prove a direct cause-and-effect relationship between full moons and human behavior.
"The one thing to realize about all these studies [that support a connection] is that correlation does not mean causation," he told ABC News. "Even if a [research] paper showed a correlation, which most do not, it wouldn't mean the moon caused the behavior." He said the only way to prove causation would be to put a human on another planet.
"To show causation, we would have to perform an experiment and control all the factors except for the moon," Chudler said. "So, for example, you would take someone to a place with no full moons like on another planet and then compare the behavior to someone in the exact situation where the moon is full."
On an award-winning neuroscience Web site for schoolchildren, Chudler explained the difference between correlation and causation this way: "If you looked for a relationship between the number of points scored by a basketball team and the number of books checked out of a library on different days, you might find a significant relationship. This doesn't mean the score of the basketball game caused people to check out library books or that checking out library books caused the basketball team to score more points. The reason why these two activities vary in a similar fashion is completely unknown and untested. It just happens that the two measurements vary in a related fashion."
Dr. David Mandell of the Children's Hospital in Pittsburgh and some colleagues studied existing data on health-care myths and did a 2005 study of area nurses. He said he found that 69 percent of surgical nurses in his study believed that a full moon led to more chaos — and patients that night.
"It is unbelievable how many nurses in southwest Pennsylvania believed in the superstitions [surrounding the full moon]," he told ABC News. But he said that it's simply part of the culture of medicine.
"In any high-stress, fast-paced field like medicine, superstitions run rampant when you feel a loss of control. This is especially true of emergency environments [because] you never know what will walk in. You need some way to explain the unpredictability of your environment," he said. "It passes on from senior to junior people in hospitals — like old times telling it to new residents coming in."
Mandell said the full moon myth isn't the only superstition pervading hospitals — he found that 78 percent of the nurses in his study believed that people with red hair were more prone to bleeding.
"Interestingly, when we asked if they considered themselves to be superstitious, only 23 percent said yes, showing that these tales have become such an ingrained part of the culture they take it as fact and common knowledge. As long as it doesn't get in the way of medical care, if it's what we need to get through the unpredictability of the job, then so be it. There's something comforting about believing in these things, even if you know that you are kidding yourself."
Rotton and others have spent years taking critical looks at other studies that claim to link the full moon to human affairs.
In 1985, Rotton and Canadian psychologist Ivan Kelly did a widely cited and extensive meta-analysis of 37 lunar effect studies and found that lunar cycles account for less than 1 percent of the variance in human activities. In 1992, according to the Canadian Medical Association Journal, two scientists reviewed 12 prominent studies conducted over 20 years that compared the number of crisis calls to the phases of the moon, and found that there was no correlation between the full moon and the frequency of calls reporting disturbing behavior.
Moonlight and Madness
The demystification of full moon myths has been a long time coming.
In the 16th century, the Swiss physician, astrologer and occultist Paracelsus wrote that "mania has the following symptoms: frantic behavior, unreasonableness, constant restlessness and mischievousness.
"Some patients suffer from it depending on the phases of the moon," according to University of Toronto psychiatry professors Alina Iosif and Bruce Ballon. In the 18th century, English legal philosopher Lord Blackstone defined the condition of lunacy as "one who hath lucid intervals, sometimes enjoying his senses and sometimes not … frequently depending upon the changes of the moon."
But there may be a simpler explanation for moon-induced behavior: moonlight. In an article on the persistence of beliefs in the lunar effect, Ballon and Iosif explain that the historic persistence of the belief has followed a relatively logical if unscientific path into the present day.
"The association between lunar phases and human behavior occupies us less today than in the past," they write. "One obvious explanation is that, before the advent of gas lighting at the beginning of the 19th century, the light of the moon permitted outdoor activities that were otherwise impossible. Full moon nights are 12 times brighter [under a clear sky] than at first or last quarter, and therefore it is likely that people stayed up later and slept less than the rest of the time. Even partial sleep deprivation can cause mania, and it is plausible that sleep disturbance during a full moon may function as positive feedback once a manic episode has begun in a predisposed person."
"Perhaps this lies at the origin of the association between madness and the full moon."