Fact Check: Does a full moon affect behaviors?

does a full moon affect behavior


FactCheck #1: Does a full moon affect people’s behaviors?

This article is part of a series by Rohit Arora. Be sure to follow Rohit on Twitter at @RealRohitArora!

Original Question

Screen Shot 2016-05-26 at 11.27.42 AM


It is a common belief that various phases of the lunar cycle, which lasts 29.5 days, have an effect on various aspects of human life such as – increased blood loss, increased violence and aggression, reproductive behavior etc (see here). In fact the terms lunacy or lunatic come from luna, the latin name for the moon. As for this particular claim, there is a general notion among medical staff that emergency room visits spike during a full moon which may be attributed to a number of reasons.

Paul J. Allegretti, DO, agrees that the emergency department seems busier when the moon is full. He’s the program director for the emergency medicine residency at Midwestern University/Chicago College of Osteopathic Medicine (MWU/CCOM) in Downers Grove, Illinois. “I think people are sicker and it seems like more unusual things happen when the moon is full, though I don’t think I could ever prove it,” he says.

But does science support the claim of a full moon affecting people’s behaviors (in terms of hospital load)? Or is it purely anecdotal?

What does science say?

Overwhelmingly the scientific studies, conducted over several decades, have shown there to be no correlation between the phase of the moon and the spike in patient admission rate in hospital emergency rooms. In addition, some studies have attempted to explain the probable reasons behind this belief.

In 1978, a literature review conducted by Campbell & Beets found no relation, in general, between any phase of the moon and the human behavior. A few positive results were attributed to a type I statistical error. Similarly, a 1985 meta-analysis of 37 studies on the topic led Rotton and Kelly to conclude that the few positive results showing link between moon-phases and human behavior can be blamed on faulty analyses. Other more recent (see here, here and suggested reading list) studies have also reached similar conclusions.

In his 2015 review article, Jean-Luc Margot (UCLA) notes:

Studies that have claimed the existence of a lunar effect universally fail to meet the reproducibility and predictability requirements

He further blames flawed data collection and analysis for a handful of studies linking moon phase and erratic human behavior. It has also been pointed out that a strong cognitive bias leading to illusory correlation and can result in erroneous conclusions.

There are however another class of studies which approach this issue differently. These studies appear to show a link between moon phases and human behavior but base their results on the notion of biorhythms, which has been shown to be a pseudoscientific concept. In fact, a technical report from NASA published In 1981 concluded:

There is no scientific basis for the “biorhythm” theory. It appears to be based on invalid mathematical principles and has been supported by studies using questionable methodology. A danger of the theory is the possibility that it can influence a person’s (a believer’s) actions by the power of suggestion. The theory has been rejected by most serious scientists involved in research of biological rhythms.

Therefore, for these studies the question of statistical errors or cognitive bias is moot.

The verdict

Based on the available scientific evidence, I rate this claim to be False.



Be sure to follow Rohit on Twitter at @RealRohitArora!

Suggested Reading

1. List of studies & data sources on the topic via Eric Chudler at University of Washington
2. Is the moon to blame? by Mona Chalabi
3. Full moon effect debunked again
by Phil Plait (discovermagazine)
4. Lunacy and the full moon (scientificamerican)
5. Biological Rhythms and Biorhythms: Science vs Pseudoscience (themadscienceblog and references therein)

Inspirational Pep Talks Don’t Cure Depression.

Eli Bosnick Atheist licking Ray Comfort

Science Enthusiast Podcast 006: Eli Bosnick Talks Atheist Activism