Family Practice
© Oxford University Press 2000
Vol. 17, No. 6
Printed in Great Britain
The effect of the full moon on general practice
consultation rates
Richard D Neal and Malcolm Colledge
Neal RD and Colledge M. The effect of the full moon on general practice consultation rates.
Family Practice 2000; 17: 472–474.
Background. 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.
Objective. 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.
Method. 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).
Results. 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.
Conclusion. 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.
Keywords. Consultation rates, full moon, general practice.
around the time of the full moon. If the hypothesis is true,
there may be major implications for the organization of
general practice and a need to intensify the search for the
mechanism underpinning this hypothesis.
Introduction
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.1 There is a body of evidence which purports
to demonstrate the effect of the full moon in relation
to health and health-related behaviours, especially with
regard to mental health. However, a meta-analysis, now
15 years old, has showed no consistent relationship.2
Two studies, both from single general practices, have
suggested that the Transylvania hypothesis does not hold
true for general practice consultations for anxiety and
depression3 or for the total out-of-hours general practice
workload.4 We set out to determine whether or not there
was any change in general practice consultation patterns
Subjects, methods and results
We analysed data from the fourth national morbidity
study of general practice,5 a valid and widely used data
set of 1 374 235 consultations from 60 practices. The
data set was split into two groups and analysed
separately: consultations on ordinary weekdays (mean
of 5276 consultations per day) and consultations on
weekends and bank holidays (mean of 371 consultations
per day). The data were split randomly into two equal
sets, one for model building and one for model
validation. The number of consultations per day was
transformed to a proportion of the daily mean for the
year, which was used as the dependent variable.
Independent variables were day of the week, month and
Received 26 January 2000; Accepted 17 July 2000.
Centre for Research in Primary Care, Nuffield Institute for
Health, University of Leeds, 71–75 Clarendon Road, Leeds
LS2 9PL, UK.
472
473
The effect of the full moon on general practice consultation rates
the lunar cycle. Day of the week and month were entered
into the regression model as categorical variables, with
Monday and January acting as reference categories. 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). Therefore we considered terms
of the formula:
 (d – f ) × π 
cos

 14.77 
where d was the number of days since the last full moon
to noon of the day whose consultations we considered;
f was an offset, indicating how far from the full moon the
maximum effect on consulting behaviour was observed;
and 14.77 was the semi-period of the lunar cycle. The
best model was one in which the maximal effect was
observed 6 days after the full moon (R2 = 0.83) (Table 1).
The best fitting curve is shown in Figure 1.
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
TABLE 1
Model term
‘Lunar’ effect
Model to predict the percentage of general practice
consultations made on a weekday
Coefficient
95% CI
P
0.018
0.009, 0.027
,0.001
Tuesday
–0.159
–0.179, –0.140
,0.001
Wednesday
–0.281
–0.300, –0.261
,0.001
Thursday
–0.247
–0.267, –0.228
,0.001
Friday
–0.204
–0.224, –0.185
,0.001
February
–0.053
–0.083, –0.023
0.001
March
–0.058
–0.088, –0.029
,0.001
April
–0.030
–0.060, 0.000
0.051
0.861
May
0.003
–0.028, 0.033
June
–0.033
–0.063, –0.004
0.028
July
–0.090
–0.119, –0.061
,0.001
August
–0.160
–0.190, –0.130
,0.001
September
–0.170
–0.199, –0.140
,0.001
October
–0.015
–0.045, 0.014
November
–0.050
–0.080, –0.021
0.001
December
–0.114
–0.145, –0.084
,0.001
Constant
1.245
1.220, 1.269
,0.001
0.297
The coefficients give the effect size as a proportion of the observed
daily mean.
FIGURE 1 The lunar effect on weekday consultations. The top graph shows the number of consultations as a proportion of the
observed daily average made on each weekday. The lower line shows the best fitting ‘lunar’ effect curve and the magnitude of its
presumed effect. The circles below it show where the full moons occurred
474
Family Practice—an international journal
cycle, or, put another way, about three consultations per
practice.
Further models were examined to see if there was
an effect from the moon on some specific morbidities
(mental illness in general, anxiety, depression); no effect
was found. We were unable to produce a meaningful
model demonstrating a lunar effect for weekends and
bank holidays.
Acknowledgements
We would like to thank Greg Cropper, whose after
dinner conversation with RDN inspired this paper, and
Brett Scaife for statistical advice and analysis. RDN
and MC are supported through the Yorkshire Primary
Care Research Network (YReN) which is funded by
NHSE Northern and Yorkshire Regional Office. The
views expressed here are those of the authors and not
necessarily those of NHSE.
Conclusions
We have demonstrated a real, if small, rise in general
practice consultations 6 days after the full moon. This
delay is presumably due to delays between the onset of
moon-related problems and behaviours, and accessing
the GP. 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.3 Our findings show that the
search for the cause of moon-related behaviour needs to
continue; but that GPs need not make special provision
for each full moon.
References
1
2
3
4
5
Trapp CE. Lunacy and the moon. Am J Psychiatry 1939; 94:
339–343.
Rotton J, Kelly IW. Much ado about the full moon: a meta-analysis of
lunar-lunacy research. Psychol Bull 1985; 97: 286–306.
Wilkinson G, Piccinelli M, Roberts S et al. Lunar cycle and consultations for anxiety and depression in general practice. Int J
Soc Psychiatry 1997; 43: 29–34.
Macdonald L, Perkins P, Pickering R. Effect of the moon on general
practitioners’ on call work load. J Epidemiol Community Health
1994; 48: 323–326.
Royal College of General Practitioners, Office of Population Censuses
and Surveys, and Department of Health. Morbidity Statistics
from General Practice—Fourth National Study 1991–1992.
London: HMSO, 1995.