IA critical thinker John Turnbull takes a look at the popularly held belief that human behaviour is effected by the phase of the moon, and whether "Full Moon Fever" really exists.

PRIOR TO the 20th century, lawyers in England could claim that their clients were "guilty by reason of the full moon", essentially an insanity defence. Indeed, the very word lunacy is based on the Latin word for moon, and many nurses and emergency response workers swear that The Lunar Effect is legitimate.

I’ve heard that hospital admittances increase during a full moon

The evidence does appear to not support this claim. While there were a few studies in the 60s and 70s that suggested a correlation between the lunar cycle and hospital admissions, every well controlled study I can find since 1980 reports no increase in admissions. These include a study of 58,000 trauma patients in Tehran, held over a period of 13 months, which reported no difference between full moon days and other days in the number of admittances or the severity of injuries treated.

A metastudy conducted back in 1985 reported:

'Correcting for errors in original reports, we found that there was no consistent relationship between phases of the moon and acts usually described as lunatic. Taken as a whole, our results confirm the generally negative conclusions reached in prior reviews'. (The Moon Was Full and Nothing Happened, I. W. Kelly, James Rotton, and Roger Culver)

On the other side of the coin, a single study from 2004 (Román, Soriano, Fuentes, Gálvez, and Fernández) suggested that the number of hospital admissions related to gastrointestinal bleeding was related to the phase of the moon, however a recent review of the data and methodology concluded:

'Their report contains a number of methodological and statistical flaws that invalidate their conclusions. Reanalysis of their data with proper procedures shows no evidence that the full moon influences the rate of hospital admissions, a result that is consistent with numerous peer-reviewed studies and meta-analyses. A review of the literature shows that birth rates are also uncorrelated to lunar phases'. (Jean-Luc Margot, No evidence of purported lunar effect on hospital admission rates or birth rates, 2015)

There was also an exceptionally credulous article written on news.com recently claiming that a University of Basel study proves the "full moon effect" has an impact on human sleep  and then goes on to detail that this is based a sample size of 33 patients. For those unfamiliar with statistical analysis and the scientific method, this is an unblinded test with far too small a sample size to provide a robust result.

But doesn’t the full moon make crazy people crazier?

While I could spend the next three hours ranting about the poor state of the mental health system in Australia, but that isn’t the subject at hand. Mental illness is a complex thing, and a change to one of any number of factors can set off an episode.

Due to this unpredicability, it is impossible to say that nobody with a psychiatric illness is impacted by the phases of the moon, particularly considering the prevalence of this belief in certain cultures. To put it another way, if a mentally ill person believes that the full moon will set them off, chances are that they’re going to be right.  

Taking this into account, there does not seems to be any credible evidence that all mentally ill people are effected by the full moon. A study of twenty years of crisis centre calls in Canada concluded:

‘No good foundation exists for the belief that lunar phase is related to the frequency of crisis calls. In addition, there is no evidence whatsoever for the contention that calls of a more emotional or "out-of-control" nature occur more often at the full moon.’ (Byrnes/Kelly Crisis calls and lunar cycles: a twenty-year review)

What about arrests? Surely criminals are more active on the full moon…

Nope, sorry. Studies of arrests during full moons reflect the same as studies of any other marker of the Lunar effect:

'There have been hundreds of such studies over the last few decades, involving emergency room visits, births, accidents, crime, crisis center calls – just about any marker of human behavior you can think of. Systematic reviews of this research consistently demonstrate that there is simply no evidence for any such effect.' (Steven Novella, Neurologica Blog)

But aren’t humans mostly water? What about the tides, smart guy?

In 1978, psychiatrist Arnold Lieber wrote a bestseller called How The Moon Affects You, which argued that it was the fact that the human body was 65 per cent water that explains the unavoidable influence of the moon.

The logic (such as it is) follows that because the moon influences the tides, it will also influence anything with a high enough percentage of water. Unfortunately, this hypothesis doesn’t hold from a scientific perspective. The reason that the moon affects the tides is the great distances involved and the vast masses of water involved there simply isn’t enough distance between the left and right side of your brain to make any difference.

This is why you don’t see watermelons rolling down supermarket aisles three nights per month.

Scientific American explains it better than I ever could:

'First, the gravitational effects of the moon are far too minuscule to generate any meaningful effects on brain activity, let alone behavior. As the late astronomer George Abell of the University of California, Los Angeles, noted, a mosquito sitting on our arm exerts a more powerful gravitational pull on us than the moon does. Second, the moon’s gravitational force affects only open bodies of water, such as oceans and lakes, but not contained sources of water, such as the human brain. Third, the gravitational effect of the moon is just as potent during new moons—when the moon is invisible to us—as it is during full moons.' (Lunacy and the Full Moon, 2009)

So why do people still believe in Full Moon Fever?

There are probably two reasons: Confirmation bias and the illusion of control.

Confirmation bias happens when you notice and remember things that reinforce beliefs that you already have, while you tend to ignore or forget contradictory data. An example of this is when a nurse might comment to a colleague that it’s crazy tonight and it must be a full moon. If it does happen to be a full moon both people will remember the incident, but if not they will likely just put it down to another busy night.

The illusion of control is a phenomenon which effects those who work in unpredictable jobs, specifically mental health and emergency workers. Because they have no objective control over the events they will face from night to night, there is a tendency to develop constructs to fall back on; Tuesday nights are quiet, full moon means crazy time, if I stop to make a cup of coffee the phone will ring. You get the idea.

In Conclusion

Based on the weight of evidence, the full moon does not have any measurable impact on human behaviour as it applies to medical, legal or psychological perspective. While a bright moon might keep you up at night, it’s highly unlikely to stimulate labour, bring on the urge to commit a crime or cause a psychotic break.

Don’t believe people when they tell you your actions are controlled by a ball of rock 384,000 km away.

Think for yourself.

Like what you just read? John’s books are now available on Amazon and Kindle. For about the price of a cup of coffee you can take a journey deep into the disturbed psyche behind columns including Screen Themes, Think For Yourself, New Music Through Old Ears and JT on NXT. There’s supernatural thriller Damnation’s Flame, action/romance Reaper, black comedy City Boy and travel guidebook Bar Trek: Europe. Check them out!

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