“The full moon causes erratic human behavior or an increase in crime.”

The enduring notion that the full moon incites peculiar human behavior or a surge in criminal activity is a concept deeply rooted in history, with its origins stretching back to ancient civilizations. The very word "lunacy" derives from "luna," the Latin word for moon, reflecting a long-held belief that the moon's phases could influence mental states. Medieval Europeans, for instance, often attributed madness and insanity to lunar cycles, with legal systems in 19th-century England even employing a "guilty by reason of the Full Moon" defense. This historical association solidified the idea of a "lunar effect" on human behavior.

Despite these persistent historical and anecdotal claims, scientific research has consistently debunked any significant correlation between the full moon and an increase in erratic human behavior, psychiatric admissions, or crime rates. Numerous studies and comprehensive meta-analyses have found no evidence to support such a link. While the moon's gravitational pull famously influences ocean tides, its effect on the much smaller bodies of water within humans is negligible and not a mechanism for behavioral changes. The few studies that initially suggested loose correlations often contained statistical errors or lacked causality.

The widespread belief in the moon's influence largely stems from a psychological phenomenon known as confirmation bias. People tend to notice and remember events that confirm their pre-existing beliefs, such as unusual occurrences during a full moon, while overlooking instances when nothing out of the ordinary happens. This selective memory is often reinforced by anecdotal evidence shared among professionals in fields like law enforcement and healthcare. Before the advent of widespread artificial lighting, the brighter full moon nights might have contributed to disrupted sleep patterns, which could, in turn, exacerbate certain conditions, further fueling the misconception.