Monday, 21 April 2008

WRONG: There's more violent crime around the full moon

Before we get down to the statistics, let’s just skip right past werewolves. We’ll also ignore the moon’s spurious connection to menstruation. (The human menstrual cycle is 28 days. The lunar cycle is 29.5 days – there is no more connection between the two than there is between the moon and a chimp’s 37-day menstrual cycle.)

The belief in a connection between the moon and human behaviour is amazingly pervasive. Even the Sussex Constabulary believes that violent behaviour increases around the full moon. In 2007, Inspector Andy Parr announced that extra police would be deployed on full moon nights, and that, “From my experience over 19 years of being a police officer, undoubtedly on full moons we do seem to get people with, sort of, stranger behaviour – more fractious, argumentative.”

Even medical staff are susceptible: Dr David Mandell canvassed the surgical nurses in his hospital in Pittsburgh in 2005 and found that 69 percent of them believed that a full moon resulted in greater social disorder and a higher number of admittances.

So what’s the cause of this apparent misbehaviour? Some would argue that it’s the “tidal pull” of the moon – if it can make the seas rise, then surely it can have an effect on beings that are predominantly composed of water, can’t it?

No, it can’t.

Everything that has mass has gravity, and gravity’s strength decreases greatly over distance. As the diligent moon-studiers Ivan Kelly, James Rotton and Roger Culver noted in their thorough demolition of full-moon myths, “A mother holding her child will exert 12 million times as much tidal force on her child as the moon”. And yet we don’t put a toddler’s tantrums down to mum’s gravitational influence.

Kelly, Rotton and Culver compared over 100 studies on the effect of the moon on behaviour and found that there was no statistically significant difference during any phase of the moon in the rates of homicide, traffic accidents, assaults, psychiatric admissions or dozens of other areas (including aggression among professional hockey players – I said they were thorough). As for the effect on mental health, they found that phases of the moon accounted for 0.03 per cent of a difference in “lunatic” behaviours. Daffodils have a more statistically significant effect on mental health.

(That was a guess. I don't have any stats on daffodils.)

While there are many studies that appear to show a connection between the moon and crime, Kelly, Rotton and Culver’s meta-analysis demonstrates that there are just as many proving the opposite. Dr Cathy Owen of Sydney University, for example, undertook an exhaustive study of aggressive behaviour among inmates of five psychiatric clinics in Sydney over six months, from “low-level threats” to assault and suicide. She and her team concluded that there was “No significant relationship between level of violence and aggression and any phase of the moon.”

Dr David Lester looked at all the violent deaths in America over a two-year period, and while he noticed that suicide was more common on Mondays and that murders tended to happen more on Saturdays, Sundays and on national holidays, there was no detectable lunar influence whatsoever.

The perception of increased bad behaviour at the full moon is most likely down to two things. First, beliefs can linger and be reinforced by communities, even police forces and hospitals, simply because they are plausible, appealing and difficult to immediately disprove. If, as a rookie policeman, you are told by an experienced officer that the nutters all come out at full moon, you’ll be likely to accept the belief, then subsequently attribute any crazy behaviour at that time to the moon, and ignore or play down identical behaviour at other times of the month.

Second, the full moon may not affect human behaviour but it certainly enables it: common sense indicates that brighter nights will encourage opportunistic criminals. This may explain the Sussex Constabulary’s figures.

While we’re on the subject of moon myths, it’s popularly held that the moon doesn’t rotate in its orbit, because if it did, we’d be able to see the “dark” side. In fact, the moon’s rotation is precisely why we only see the man in the moon – to a greater or lesser degree – every night: the moon spins exactly once for every orbit it makes of the earth. If you’re having trouble visualising this, draw a face on a grapefruit (or tennis ball, or sea urchin – amazingly it makes no difference) and “orbit” it around your finger while keeping the face looking at the finger. You’ll notice that you have to revolve it to do so. If you didn’t, your finger would see the dark side of the grapefruit.

The dark side of the moon, by the way - or the far side as astronomers prefer - is only dark during the full moon – it sees as much of the sun as the familiar side, but we never get to look at it ourselves from earth. According to astronaut William Anders, who orbited the moon, “The backside looks like a sand pile my kids have played in for some time. It's all beat up, no definition, just a lot of bumps and holes.” Here it is.

1 comment:

Nicholas Courtenay said...

Just for this post alone, you deserve big kudos.

This bollocks gets repeated all the time.