Does Crime Increase When the Moon is Full?

Just in time for Halloween, the BetaGov team at NYU's Marron Institute of Urban Management is releasing a three-country study on the "lunar effect."

Betagov, which carries out randomized controlled trials for, and collaborates with, stakeholders in the field, looked into the purported relationship between crime and the full moon. The investigation resulted from a conversation with a police official in Vallejo, CA, and an article on the phenomenon he pointed out from Australia.

To start out, BetaGov researchers conducted a review of the overall research literature on the "lunar effect," which, surprisingly, is mixed. Some studies have found evidence of a lunar effect on crime and negative behavior, and others show none at all.

The Vallejo police official, meanwhile, pulled together his agency's crime data from January 2014 through May 2018. He researched phases of the moon for each crime event, and sent BetaGov his data for analysis. According to the analysis, 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.

Other police departments heard about this analysis and were curious whether there was evidence for the lunar hypothesis in their own data. To make sure North America was represented, BetaGov teed up replication studies with the Barrie (Ontario) Police Service in Canada and the Irapuato Citizen Safety Secretariat in Mexico. The team merged moon-phase data into their calls-for-service and crime data.

What was found? Again, nothing.

"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," said BetaGov director Angela Hawken (PhD), a professor of public policy at the NYU Marron Institute.