Correlating Crime Data with Full Moons

Full moons are steeped in legends and traditions.
Full moons are steeped in legends and traditions.

There was a point in medical history when doctors and health professionals almost universally believed in a strong connection between human psychology and moon phases. Full moons have been associated with anomalies like  sleepwalking, mania, and even illegal activity. The term lunar effect refers to the relationship between the moon’s cycle and our behavior. I wanted to explore whether the lunar effect has any merit when its pertains to crime,  so I downloaded the last 33 months of crime data from the Atlanta Police Department (APD) to see if I could find a data correlation between full moons and reported crimes.

Digging into the Data

The hypothesis I set out to prove was relatively simple: a data correlation will exist if more crimes are reported on dates with a full moon than the dates immediately before and after a full moon.  To quantify my hypothesis I aggregated the APD data by month and I counted the number of reported crimes immediately before, during, and immediately after the full moon of each month. The charts below illustrate how many crimes were reported around full moon days for 2015 – 2017.

2017 (January – September)
Months with more reported crimes on full moon dates vs previous and next dates: 3 out of 9 (33%)

2017 Crimes Reported before, during and after a full moon.
2017 Crimes Reported before, during and after a full moon.

2016
Months with more reported crimes on full moon dates vs previous and next dates: 2 out of 12 (17%)

2016 Crimes Reported before, during and after a full moon.
2016 Crimes Reported before, during and after a full moon.

2015
Months with more reported crimes on full moon dates vs previous and next dates: 5 out of 12 (42%)

2015 Crimes Reported before, during and after a full moon.
2015 Crimes Reported before, during and after a full moon.

2015 – 2017 Combined
Months with more reported crimes on full moon dates vs previous and next dates: 4 out of 9 (44%)

2015 - 2017 Crimes Reported before, during and after a full moon.
2015 – 2017 Crimes Reported before, during and after a full moon.

Note: 2017 is a partial year as of this writing.  Based on historical data, I project 2017 will end with 3 out of 9 (25%) months with more reported crimes on full moon dates vs the previous and the next dates.

By the Numbers

Lets go a bit deeper and look at the actual APD counts. The chart below shows the number of reported crimes during the full moon dates for 2015 – 2017. This will give you an sense of the sample size of the data being evaluated. To add some flavor, I have included the traditional Native American names for each full moon as listed by The Old Farmer’s Almanac.

Reported crimes during a full moon. 2015 - 2017
Reported crimes during a full moon. 2015 – 2017

Now lets look at how the previous and next dates compared to the numbers above. The chart below lists the percentage of increase or decrease in the number of crimes reported to APD on full moon dates vs the date immediately before a full moon.  The numbers highlighted in red call-out the months where the full moon counts were 2% or greater than the previous day counts.

Reported crimes before a full moon. 2015 - 2017
Reported crimes before a full moon. 2015 – 2017

The chart below lists the percentage of increase or decrease in the number of crimes reported to APD on full moon dates vs the date immediately after a full moon.  The numbers highlighted in red call-out the months where the full moon counts were 2% or greater than the next day counts.

Reported crimes after a full moon. 2015 - 2017
Reported crimes after a full moon. 2015 – 2017

The Bottom Line

My experiment is an admittedly small sample size, and there are many other caveats we could consider when answering whether a full moon affects human behavior.  However, if we use my analyses as a proxy for a larger data set, then it is easy to see that a full moon  has no bearing on crime.

The chart below summarizes the months that had higher reports on full moon dates than the dates before and after a full moon.

Summary of reported crimes during a full moon. 2015 - 2017
Summary of reported crimes during a full moon. 2015 – 2017

On a much grander scale, Florida International University psychologist James Rotton, Colorado State University astronomer Roger Culver and University of Saskatchewan psychologist Ivan W. Kelly have conducted extensive research on this subject. In their 1985 review entitled “Much Ado about the Full Moon” which appeared in the Psychological Bulletin, Rotton and Kelly concluded that there is no credible link between moon phases and human behavior but “psychologists need to take the topic seriously because, if for no other
reason, so many people believe that their behavior is influenced by the moon”.

My conclusion agrees with Rotton and Kelly. Though many full moon legends and scores of Hollywood scenes depict strange happenings (and even werewolf transformations) during full moons, I find no evidence of a solid correlation between moon phases and reported crimes. I will try and keep this in mind as I’m watching my next Stephen King movie.

“The reason for full moons is so the gods can more clearly see the mischief they create.”
Michael J. Sullivan

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