The lunar effect

Hard to keep a good myth down

A recent study done at the Colorado State College of Veterinary Medicine was reported this year in the July publication of the Journal of the American Veterinary Association. Canine and feline emergency room visits and the lunar cycle: 11,940 cases (1992-2002) evaluating whether the full moon influences activity at the emergency hospital is a retrospective study that includes 11,940 dogs and cats over an eleven year period. A variety of emergency admissions were associated with their corresponding lunar phase based on the date of the visit. The lunar phases were divided into new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, or waning crescent. The effect of lunar phase on the frequency of these visits was evaluated by calculating relative risk.

The authors conclude that there is indeed an association with emergency admissions and the lunar cycle. They identified a significant increase in admissions of both species during “fuller” moon days (waxing gibbous to waning gibbous). Interestingly, the clinical relevance section of the study notes that “It is unlikely that an attending clinician would notice the fractional increase in visits (0.59 and 0.13 more canine and feline visits, respectively) observed in this study at a facility with low caseload.” They do suggest that this data set implies that at a “larger facility with a robust emergency caseload, these results may lead to reorganization of staffing on fuller moon dates.” However, we need to take a step back and take a larger look at this whole lunar association issue before accepting these findings as relevant.

The idea that there is some association between the fluctuating phases of the moon and animal or human behavior goes back eons and is fairly well established within the pages of common folklore crossing all kinds of cultures and continents. Even now, in modern times it is not uncommon to associate the phases of the moon with changes in any number of activities, including those found in a medical setting such as emergency visits at a veterinary hospital.

Therefore, this Colorado study joins a long and interesting lineage of similar studies that concern themselves with the possible effects of the lunar cycle with animal or human medical events. This is an important detail as it will become apparent that this particular study needs to take its place among the plethora of other such studies and be considered a small part of a larger body of information before actions such as adjusting the veterinary staff can be made.

A comprehensive review by Kelly et al ¹ went over a variety of human studies that examined a possible relation between the cycles of the moon and abnormal behavior. Using statistical methodologies including meta-analysis and additionally reanalyzing previous published studies, the authors found a variety of significant errors that biased many conclusions in favor of a positive association. As noted by the authors, a meta-analysis is only as good as the information on which it is based (garbage in/garbage out), and it is crucial to make an effort to evaluate each study for any statistical errors. Besides being only one study, the Colorado conclusion needs to be evaluated carefully for errors or confounding factors. All these items will help shake out its ultimate value among the sea of data out there.

Another non-meta-analysis review² in humans found “no evidence of a trend for more calls to be reported around the full moon. The majority of studies yielded no relationship between lunar phase and crisis calls and the positive findings contradicted each other.” Interestingly a 1996 study³ as well as others found a correlation between weekly, annual, and semi-weekly cycles (i.e.; Time of day and weekdays- makes sense) but no relation to lunar cycles. Additionally, a variety of related studies (birth rates, personality traits, aggression in sports) also reveal no significant relationship between lunar cycle and the data points being considered.

This year, there was another recent animal study regarding the full moon and veterinary emergency visits done at the University of Melbourne Veterinary Clinic and Hospital Australia. This retrospective study evaluated 12,102 animal admissions between 2003 and 2006 on full moon and non-full moon days adjusting for the day of the week and public holidays.

This study found no significant difference between the number of animals presented to the emergency clinic between full and non-full moon days. This study is especially interesting because of the adjustments they make for days of the week and holidays which may be a confounding factor in the Colorado study not accounted for.

As a whole, these findings put a damper on any definite positive conclusions the Colorado study might have found, however slight. The overall conclusion at this point then continues to be that there is no significant relation between the lunar cycle and a variety of associations in humans or animals including emergency admissions.

1 The Moon was Full and Nothing Happened. Skeptical Inquirer Winter 1985-86, updated 1996.

2 Byrnes, G & Kelly, I. Crisis calls and lunar cycles: A twelve year review. Psychological Reports, 71,779-785.

3 Bickis M , M Kelly I, et al. Crisis calls and temporal and lunar variables: a comprehensive examination. The journal of psychology 1995 , 129,701-711.