The effect of the full moon on general practice consultation rates

The effect of the full moon on human behaviour, the so-called 'Transylvania hypothesis', has fascinated the public and occupied the mind of researchers for centuries.

The aim of the present study was to determine whether or not there was any change in general practice consultation patterns around the time of the full moon.

We analysed data from the fourth national morbidity study of general practice. The data set was split into two groups and analysed separately: consultations on ordinary weekdays and consultations on weekends and bank holidays. The data were split randomly into two equal sets, one for model building and one for model validation. The lunar cycle effect was assumed to be sinusoidal, on the grounds that any effect would be maximal at the time of the full moon and decline to the new moon, following a cosine curve (with a period of 29.54 days, the mean length of a lunar cycle).

There was a statistically significant, but small, effect associated with the lunar cycle of 1.8% of the mean value [95% confidence interval (CI) 0.9-2.7%]. This equates to an average difference between the two extremes during the cycle of 3.6%. For this data set, this accounts for 190 (95% CI 95-285) more consultations on days at the peak of the cycle compared with those at the bottom of the cycle, or, put another way, about three consultations per practice.

We can speculate neither as to what the nature of these moon-related problems may be, nor as to the mechanisms underpinning such behaviour. However, we have confirmed that it does not seem to be related to anxiety and depression.