In a article by USA Today, several studies were evaluated in respect to the effect of the full moon and violent crimes and the like. It has always been an urban legend that the full moon incites insanity and malcontent, which most anecdotal evidence will confirm. However, all anecdotal evidence is highly subjective, and usually inconsistent. What the article says in summary is that there is no link between the full moon’s presence and the variables tested. The anecdotal evidence is then explained by the fact that many of the reporters are subject to belief in the paranormal.
Why specifically does everyone think this is true? Everybody falls victim to the confirmation bias. It states:
A tendency for people to favor information that confirms their preconceptions or hypotheses regardless of whether the information is true.
Why do the police think there is more crime when the full moon is out? Because they believe it to be true in the first place, and furthermore they heavily remember the times crime happened under a full moon, and forgot when it didn’t. This bias derails many pseudoscience arguments. It has been proven that if you start out with a belief, and try to verify that belief, you will find “evidence” even if there really is no connection. This includes bigfoot, ufo, and ghost related claims.
Think about it. When you were a child and believed in Santa Claus, wasn’t it easy to rationalize his existence? Even though it was (spoiler alert) the work of the parents, it was very easy to see all the evidence that he existed, and to block out or ignore the evidence that he did not.
“That sure looks like my dad’s boot print, but of course it isn’t his because it is Santa’s!“
A tendency to believe in the supernatural seems to be a part of the human condition. Through critical thinking it is possible to be objective and to evaluate reasonable evidence to make a conclusion. In this case the evidence has not been in the public knowledge, and articles like this can help. A lot of good science does make the effect of the moon seem very powerful. Everything from the moon’s interactions with the Earth’s magnetosphere, to the interaction of tidal forces controlled by the moon. These legitimate claims, unlike the crime spree arguments, do hold water when evaluated with the evidence.
Sadly, we will just have to blame the crazies of the night on their own brains, like rational folks.