Friday, December 12th is a full moon. Spooky effects have been ascribed to that phase of the moon, but statistics do not a show correlation of events to lunar phases.
The full moon has been linked to crime, suicide, mental illness, disasters, accidents, birthrates, fertility, and werewolves, among other things. Some humans even buy and sell stocks according to phases of the moon, a method probably as successful as many others. Numerous studies have tried to find lunar effects. So far, the studies have failed to establish much of interest. Lunar effects that have been found have little or nothing to do with human behavior. Of course, there have been single studies here and there that have found correlations between various phases of the moon and this or that phenomenon, but nothing significant has been replicated sufficiently to warrant claiming a probable causal relationship. (A study in the year 2000 showed a correlation between binge drinking and the full moon, but that is likely do more to humans acting out their superstitious natures than it is to any influence by the moon.)
Ivan Kelly, James Rotton and Roger Culver (1996) examined over 100 studies on lunar effects and concluded that the studies have failed to show a reliable and significant correlation (that is, one not likely due to chance) between the full moon, or any other phase of the moon, and each of the following:
-the homicide rate
-crisis calls to police or fire stations
-births of babies
-casino payout rates
-aggression by professional hockey players
-violence in prisons
-psychiatric admissions [one study found admissions were lowest during a full moon]
-agitated behavior by nursing home residents
-emergency room admissions
-behavioral outbursts of psychologically challenged adults
If so many studies have failed to prove a significant correlation between the full moon and anything, why do so many people believe in these lunar myths? Kelly, Rotton, and Culver suspect four factors: media effects, folklore and tradition, misconceptions, and cognitive biases. A fifth factor should be considered, as well: communal reinforcement.
Lunar myths are frequently presented in films and works of fiction. "With the constant media repetition of an association between the full moon and human behavior it is not surprising that such beliefs are widespread in the general public". Reporters also "favor those who claim that the full moon influences behavior." It wouldn't be much of a story if the moon was full and nothing happened, they note. Anecdotal evidence for lunar effects is not hard to find and reporters know that one good anecdote trumps ten scientific studies when it comes to reader interest, even though such evidence is unreliable for establishing significant correlations. Relying on personal experience ignores the possibility of self-deception and confirmation bias. Such evidence may be unreliable, but it is nonetheless persuasive.
Many lunar myths are rooted in folklore. For example, an ancient Assyrian/Babylonian fragment stated that "A woman is fertile according to the moon." Such notions have been turned into widespread misconceptions about fertility and birthrates. The belief that there are more births during a full moon persists today among many educated people. Many delivery room nurses for example, swear that they are busier during a full moon despite physical evidence to the contrary.
Scientific studies have failed to find any significant correlation between the full moon and the number of births. In 1991, Benski and Gerin reported that they had analyzed birthdays of 4,256 babies born in a clinic in France and "found them equally distributed throughout the synodic (phase) lunar cycle". In 1994, Italian researchers Periti and Biagiotti reported on their study of 7,842 spontaneous deliveries over a 5-year period at a clinic in Florence. They found "no relationship between moon phase and number of spontaneous deliveries".
What we do know is that there has been very little research on hormonal or neurochemical changes during lunar phases. James Rotton's search of the literature "failed to uncover any studies linking lunar cycles to substances that have been implicated as possible correlates of stress and aggression,. One would think that this area would be well-studied, since hormones and neurochemicals are known to affect menstruation and behavior.
Misconceptions about such things as the moon's effect on tides have contributed to lunar mythology. Many people seem to think that since the moon affects the ocean's tides, it must be so powerful that it affects the human body as well. The lunar force is actually a very weak tidal force. A mother holding her child "will exert 12 million times as much tidal force on her child as the moon". Astronomer George O. Abell claims that a mosquito would exert more gravitational pull on your arm than the moon would. Despite these physical facts, there is still widespread belief that the moon can cause earthquakes.
It doesn't; nor does the sun, which exerts much less tidal force on the earth than the moon.
The fact that the human body is mostly water largely contributes to the notion that the moon should have a powerful effect on the human body and therefore an effect on behavior. It is claimed by many that the earth and the human body both are 80% water. This is false. Eighty percent of the surface of the earth is water. Furthermore, the moon only affects unbounded bodies of water, while the water in the human body is bounded.
Also, the tidal force of the moon on the earth depends on its distance from earth, not its phase. Whereas the synodic period is 29.53 days, it takes 27.5 days for the moon to move in its elliptical orbit from perigee to perigee (or apogee to apogee). Perigee (when the moon is closest to earth) "can occur at any phase of the synodic cycle".
Higher tides do occur at new and full moons, but not because the moon's gravitational pull is stronger at those times. Rather, the tides are higher then because "the sun, earth, and moon are in a line and the tidal force of the sun joins that of the moon at those times to produce higher tides".
Many of the misconceptions about the moon's gravitational effect on the tides, as well as several other lunar misconceptions, seem to have been generated by Arnold Lieber in "The Lunar Effect" (1978), republished in 1996 as "How the Moon Affects You". In "The Lunar Effect", Lieber incorrectly predicted a catastrophic earthquake would hit California in 1982 due to the coincidental alignment of the moon and planets. Undeterred by the fact that no such earthquake had occurred, Lieber did not admit his error in the later book. In fact, he repeated his belief about the dangers of planet alignments and wrote that they "may trigger another great California earthquake." This time he didn't predict when.
Beliefs and Communal Reinforcements
Many believe in lunar myths because they have heard them repeated many times by members of the mass media, by police officers, nurses, doctors, social workers, and other people with influence. Once many people believe something and enjoy a significant amount of communal reinforcement, they get very selective about the type of data they pay attention to in the future.
If one believes that during a full moon there is an increase in accidents, one will notice when accidents occur during a full moon, but be inattentive to the moon when accidents occur at other times. If something strange happens and there is a full moon at the time, a causal connection will be assumed. If something strange happens and there is no full moon, no connection is made, but the event is not seen as counter evidence to the belief in full moon causality. Memories get selective, and perhaps even distorted, to favor a full moon hypothesis.
A tendency to do this over time strengthens one's belief in the relationship between the full moon and a host of unrelated effects.
The moon, madness and suicide
Probably the most widely believed myth about the full moon is that it is associated with madness. However, in examining over 100 studies, Kelly et al. found that "phases of the moon accounted for no more than 3/100 of 1 percent of the variability in activities usually termed lunacy". According to James Rotton, "such a small percentage is too close to zero to be of any theoretical, practical, or statistical interest or significance".
Finally, the notion that there is a lunar influence on suicide is also unsubstantiated. Martin et al. reviewed numerous studies done over nearly three decades and found no significant association between phases of the moon and suicide deaths, attempted suicides, or suicide threats. In 1997, Gutiérrez-García and Tusell studied 897 suicide deaths in Madrid and found "no significant relationship between the synodic cycle and the suicide rate".
These studies, like others which have failed to find anything interesting happening during the full moon, have gone largely unreported in the press.
(So sadly, it is unlikely that my human will grow fur on Friday and start running around, barking on all fours. Of course, that certainly would have been interesting...)