What the studies found
Rotton and Kelly aggregated 37 studies covering homicides, other criminal offenses, psychiatric admissions, crisis calls, and disaster reports. Lunar phase accounted for a negligible share of variance, and the small effects that did appear were attributable to methodological artifacts rather than the moon. Subsequent reviews of police and hospital data have generally reached the same place.
Why the belief persists
- Confirmation bias — a busy full-moon shift is memorable; a busy new-moon shift is just Tuesday.
- Illusory correlation — we pair a vivid cue with a vivid outcome and stop counting the misses.
- Occupational folklore — the belief is passed along as shared knowledge in shift work, which makes it feel corroborated.
- Real confounds — weekends, paydays, holidays, and warm weather do move arrest volume, and those cycles occasionally line up with a full moon.
What actually predicts a busy night
From the bail side, the patterns are unglamorous: Friday and Saturday nights, holiday weekends, and major events. Those are the nights county intake backs up and release times stretch — see how long after posting bail is an inmate released and are bail bonds open on the weekend.