There Was a Full Moon and Nothing Happened . . . Again

Jean-Luc Margot (March 29, 2015)

What is this article about?

Some professionals who work in emergency rooms or maternity wards believe that the number of hospital admissions or human births is larger during the full moon than at other times.

This belief is incorrect. Analysis of the data shows conclusively that the moon does not influence the timing of hospital admissions or human births. An article describing the results of a new analysis was published online in the journal Nursing Research in March 2015.

Why should anyone care?

The study illustrates how intelligent and otherwise reasonable people develop strong beliefs that are not aligned with reality.

Allowing your brain to develop beliefs that are inconsistent with indisputable facts is poor brain hygiene. It's like allowing your teeth to decay.

Why worry about erroneous beliefs?

Beliefs often dictate actions. The societal costs of flawed beliefs are enormous. For instance:

  • Health professionals have been struggling to contain an outbreak of measles because of questionable beliefs related to the safety of vaccines. Vaccines are widely and correctly regarded as one of the greatest public health achievements, yet vaccine-preventable diseases are killing people because of beliefs that are out of step with scientific facts.
  • In December 2014, news reports described the imminent extinction of the northern white rhinoceros because of high demand - driven by human superstition - for rhinoceros horns.
  • Polar bears and other species are in danger of becoming extinct because of incorrect beliefs about the reality of climate change. The evidence for climate change caused by human activity is irrefutable, yet lawmakers continue to delay taking corrective action and cite, for instance, the presence of snow in winter to support their unfounded beliefs.
  • Throughout the world, people have invoked religious beliefs as justification for horrific violence and destruction. Throughout history, millions of people have been executed based on these unsound beliefs, a reality that we still face today. Religious beliefs are also at the root of the recent destruction of archaeological treasures such as in the Assyrian city of Nimrud and the Buddahs of Bamiyan.

How prevalent is this problem?

A 2005 Gallup poll reveals that 3 out of 4 Americans believe in at least one unfounded concept (e.g., ghosts, witches, astrology, etc).

A dozen surveys conducted over the past 30 years show that 4 out of 10 Americans believe that humans were created in the last 10,000 years.

As many as 6% of Americans believe that the Apollo moon landings were faked. A major television network even produced a documentary to feed this conspiracy theory nonsense.

What can we do about it?

Increasing your education level is not sufficient. Studies have shown that even highly educated people have questionable beliefs.

Promoting sound habits of mind (i.e., critical thinking) is important but difficult. Some of the built-in processes in the brain tend to yield erroneous conclusions (see Thomas Gilovich's How We Know What Isn't So or Daniel Kahneman's Thinking, Fast and Slow). It takes effort and discipline to maintain good mental (or dental) hygiene.

Adopting a humble attitude is essential. Acknowledge the possibility that some of your beliefs may be misguided.

Allow yourself to change your beliefs. The willingness to revise beliefs is necessary to secure a more accurate view of the world. The method that has given us automobiles, cell phones, and decades of increased life expectancy relies on examining beliefs and abandoning them, as necessary.

Rely on evidence and reason. Examine claims skeptically (note: denialism - burying one's head in the sand - is not the same as skepticism). Ask yourself how a claim could be proven wrong. Can you think of a counter-example? Are there any premises or steps in an argument that are flawed?

Be aware of the confirmation bias. We have a tendency to interpret information in a way that confirms our beliefs and to ignore data that contradict our beliefs. What are the facts? Review all the evidence, especially the evidence that seems to refute your beliefs.

Enjoy the benefits. Being able to distinguish fact from hogwash is liberating and empowering. Clearer thinking will enable you to make better decisions, which will improve the quality of your life. (Some of the statements on this page are opinions, of course. I am not advocating abandoning all beliefs and opinions, but I am encouraging a deeper examination of the evidence that supports beliefs.)

How did I get interested in this problem?

In 2013, I had a pleasant reunion dinner with high school friends. The dinner host is a midwife and midwife trainer, and she insisted that the number of deliveries increased when there was a full moon. I was baffled. Surely she must have known about the numerous studies demonstrating that the moon had no such influence. She is an intelligent and otherwise reasonable person. How could her belief be so disconnected from reality?

A few weeks later, I found that a similar claim had somehow made its way into the peer-reviewed literature. A group of health care professionals in Barcelona, Spain, claimed that the number of admissions at their hospital unit was larger on "full moon days," and a nursing journal published this claim in 2004. This article is flawed but had remained unchallenged. Something had to be done.

While I sought to dispel myths about the moon, I was also motivated by the fact that questionable beliefs are at the root of many of society's worst problems. Could the lessons learned about flawed beliefs related to the moon be applied to a broader context?

What was wrong with the 2004 study?

Almost everything, regrettably. This made it relatively easy to debunk the claim and provided an opportunity to describe how one could conduct a similar study in a rigorous manner. (This is not something that I encourage as it has been done many times.)

There were problems with the authors' understanding of the lunar cycle. They naively assigned admissions at their hospital unit to one of 29 days, but the duration of the lunar cycle varies! Over the duration of their study, the time interval between consecutive full moons reached a minimum of 29.28 days and a maximum of 29.80 days. Currently, the average length of the cycle of lunar phases is roughly 29.53 days. The data collection procedure in the 2004 study biased the results.

The authors failed to consider periodicities or trends present in the data but unrelated to the moon, such as day-of-week variability. Failure to control for these effects can result in a genuine variability masquerading as a lunar cycle variability - something that previous studies about the frequency of car accidents had recognized.

There were problems with the statistical tests that the authors used; some assumptions of the tests were violated, which rendered the tests meaningless. The authors also used a fairly low level of statistical confidence. At such low levels, it is not unusual to "detect" an effect that is not present, an error known as a "type I" error. Carl Sagan popularized the concept that "extraordinary claims require extraordinary evidence," and this was an extraordinary claim with mediocre evidence.

The authors noted something that they felt was anomalous, but they failed to verify whether this anomaly was truly associated with the moon. For instance, if anomalies occurred at random times during the lunar cycle, the moon would have to be exonerated. The data showed that there were anomalies on days 9, 12, 13, 27, and 29 of the authors' lunar calendar, indicating that the full moon could not possibly be responsible.

The interpretation that the authors proposed in their study was also incorrect. They invoked the strength of lunar tides on blood as a possible explanation for the purported lunar effect. Their attempted explantaion underscores misconceptions about tides. First, tides act on ordinary matter, whether liquid or solid. Second, the strength of tides is proportional to the mass of the tide-raising body and inversely proportional to the cube of the distance from the tide-raising body. Therefore, ordinary objects (e.g., cars, houses, hospitals, etc.) in the vicinity of a potential patient exert tides that are orders of magnitude stronger than those exerted by the moon. In addition, the strongest lunar tides occur at both new moon and full moon (when the Sun, Earth, and Moon are roughly aligned), but an increase in hospital admissions at new moon was not observed, further invalidating the interpretation.

How difficult was it to publish a rebuttal?

Publishing my article debunking the purported lunar effect was considerably more difficult than publishing any of my scientific work. It was important to publish the rebuttal in a nursing journal in order to reach the intended audience, but several nursing journals did not want to touch this subject with a 10-foot pole - not because reviewers thought that the scholarship was lacking, but because journal editors did not even want to seek the appraisal of reviewers.

  • The International Journal of Nursing Practice, where the 2004 study had been published, "unsubmitted" (their word) my manuscript three times, after which I gave up resubmitting it.
  • The International Journal of Nursing Studies rejected the paper two days after submission in October 2013 with a polite note from the editor: "The Editorial Committee considered your paper. Although we found it interesting it did not attract sufficient support for us to send it out for peer review. This sometimes happens with perfectly good papers which we are unable to make a priority to publish because competition for space is high or the fit to the journal's aim is not sufficiently close." Fair enough.
  • The journal Nursing Outlook considered the paper for five weeks, then rejected it with the following note: "While this is an interesting topic it is not consistent with the editorial purpose of NO. Therefore I must reject the manuscript without sending it out for review."
  • The American Journal of Nursing considered the paper for four weeks, then rejected it with the following note: "Thank you for the opportunity to review your manuscript. After careful review, however, we feel your paper is not a good fit for our journal at this time."
  • I am grateful to the editor at Nursing Research because she had the courage to explore this incorrect yet pervasive belief in the nursing community. The manuscript was submitted on December 30, 2013. I received the reviews on May 20, 2014 and submitted a revised manuscript on August 11, 2014. The manuscript was accepted on September 8, 2014 and appeared online in March 2015.

Retraction Watch blog article

The folks at Retraction Watch published a story titled "Why publishing negative findings is hard". The story describes my attempts to set the record straight about two controversial claims related to the effects of the full moon, including the extraordinary claim that a plant pollinates during the full moon.

Retraction Watch interviewed the editors of the nursing journals that rejected my paper. The editor of the journal that published the 2004 hospital admission study sought to distance herself from the journal's editorial decision: "I welcome discussion and critique of papers published in the International Journal of Nursing Practice, but would prefer to focus on current rather than historical pieces." Are we expected to absolve the journal from publishing shoddy work in 2004, as if that was some kind of ancient era that nobody is accountable for? My 2013 submission to IJNP did not seem that welcome. It was "unsubmitted" (whatever that means) three times.

Press coverage

A press release was written by UCLA's Stuart Wolpert. A Spanish version is available.

A blogger erroneously reported that I was responsible for suggesting that astronomers ought to be included in studies of purported lunar effects. This suggestion was not present in my original manuscript and it was added in the revised manuscript at the express request of the journal editor. Even though it was not my idea, I believe that the editor's recommendation is wise.