This week I’ll be doing a special 5-part series of spooky Halloween-related myths.
Today’s myth: The full moon effect.
Many people believe that the full moon causes strange things to happen. A crime may be committed, or there is an odd occurrence, and someone might say “it must be a full moon”. Folklore tales spread the belief that the moon causes insanity, hence the term “lunacy”. The moon is also linked to various myths such as werewolves.
But a 1986 meta-analysis of “the full moon effect” by Kelly, Rotton, and Culver found that there was no increase in crime, accidents, lunacy, symptom exacerbation, sex, aggression, suicide, etc. during the full moon. Other research has similarly shown no effect.
So, why do people believe there is a moon effect?
To set the tone of the explanation for this apparent phenomenon, I refer you to this comic about the primary full moon logical error. This error is called confirmation bias. Essentially, odd events that happen on a full moon are remembered more saliently than on other days, and uneventful full moons are not remembered. This leads to the false conclusion that more odd events happen on the full moon than on other days.
Another explanation is the confusion between correlation and causation. It is possible for odd events to happen on a full moon, but not be caused by the full moon. This is a very common error in thinking, as humans tend to seek patterns and explanations for events.
Finally, there is much folklore and tradition surrounding the full moon effect. The moon is a salient feature in the sky that people are very familiar with. Stories and attitudes about the moon are pervasive in our society. Especially with so many events approximately associated with the moon: the calendar month, menstruation, tides, etc.
But even though it’s very sexy with the moonlight and craziness, there is no moon effect.
UPDATE: Here is another article about the full moon effect.