Does a Full Moon Really Inspire More Crime?

©. robert_s

Researchers look into whether the 'lunar effect' is based on superstition or empirical data.

It's unclear where the idea first came from, but the superstitious have long held that the full moon brings about changes in human behavior. It has even been codified in language, as noted in the every-wonderful Online Etymology Dictionary:

lunatic (adj.): late 13c., "affected with periodic insanity dependent on the changes of the moon," from Old French lunatique "insane," or directly from Late Latin lunaticus "moon-struck," from Latin luna "moon" (see luna).

Known as the "lunar effect," the full moon is said to give rise to spikes in crime (as well as admissions to psychiatric hospitals). While one might imagine that the full moon would have the opposite effect – at least in pre-industrial times, it seems that more light would lead to less crime – yet the myth has persisted. So, perhaps from its increased light and effect on gravity, could the moon's power actually be nudging us toward untoward behavior?
This is the question put forth to the BetaGov team at NYU's Marron Institute of Urban Management, who have now published a paper on the topic.

It all began with a chat about the phenomenon between BetaGov and a curious police official in Vallejo, California. BetaGov's mission is to "help policymakers and government agencies identify problems, develop innovative solutions, and test them using rigorous research methods" – making this a perfect case for the researchers. If the data confirms increases in crime, there are practical policy considerations that law enforcement may want to consider.

The researchers started by reviewing existing research literature on the lunar effect – finding that some studies have found a connection between a full moon and crime, while others show none at all.

Meanwhile, the Vallejo police official compiled crime data from his area for January 2014 through May 2018, which was compared to moon phase data. After BetaGov analyzed the data, they concluded that:

"...the data demonstrated that there's no association between crime events and full moon. In Vallejo, California, at least, people don't commit more crimes when there is a full moon."

But what about other parts of the world? Could Vallejo simply be an outlier?

So the researchers ran the same data analysis with the Barrie (Ontario) Police Service in Canada and the Irapuato Citizen Safety Secretariat in Mexico, comparing moon-phase data with emergency calls and crime data.

The results were consistent with Vallejo's: No evidence of a connection was found. All told, "There was no statistically significant difference in the number of calls for police service during full-moon days compared with non-full-moon days."

(And by the way, similar conclusions have been found about a connection between lunar phases and psychiatric hospital admissions.)

Debunking "false facts" is always amusing in a "wow" kind of way, but basing policy on superstitions and assumptions is obviously not the most prudent approach. As BetaGov director Angela Hawken from the NYU Marron Institute notes:

"Although these kinds of analyses are fun, the findings have practical implications for policing such as in developing staffing assignments and distribution of other law-enforcement resources. The bottom line is be vigilant in questioning your assumptions and use your data to explore. It might just surprise you."

Fair enough ... now about those werewolves.