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ORIGINAL SCIENTIFIC REPORTS
Popular Belief Meets Surgical Reality: Impact of Lunar Phases,
Friday the 13th and Zodiac Signs on Emergency Operations
and Intraoperative Blood Loss
Jochen Schuld •Jan E. Slotta •Simone Schuld •
Otto Kollmar •Martin K. Schilling •
Sven Richter
Published online: 29 June 2011
ÓSocie
´te
´Internationale de Chirurgie 2011
Abstract
Background The influence of superstition, moon calen-
dars, and popular belief on evidence-based medicine is
stunning. More than 40% of medical staff is convinced that
lunar phases can affect human behavior. The idea that
Friday the 13th is associated with adverse events and bad
luck is deep-rooted in the population of Western industrial
countries. The aim of the present study was to test the
hypothesis that these myths are transferable to real-life
surgery.
Methods We analyzed the extent to which moon phases,
zodiac signs, and Friday the 13th influence blood loss,
emergency frequency, and intestinal perforations by eval-
uating the operation records of all 27,914 consecutive
patients of our institution undergoing general, visceral, or
vascular surgery between August 2001 and August 2010.
Dates of surgery were allocated to lunar phases and to
zodiac signs, as well as to Friday the 13th.
Results A total of 111 lunar cycles and 15 Fridays the
13th occurred within the 3,281-day observation period.
Patients’ characteristics did not differ in lunar phases,
zodiac signs, or Fridays the 13th. Full moon phases, the
presence of Friday the 13th, and zodiac signs influenced
neither intraoperative blood loss nor emergency frequency.
No statistical peaks regarding perforated aortic aneurysms
and gastrointestinal perforations were found on full moon
or Friday the 13th.
Conclusions Scientific analysis of our data does not
support the belief that moon phases, zodiac signs, or Friday
13th influence surgical blood loss and emergency fre-
quency. Our data indicate that such beliefs are myths far
beyond reality.
Introduction
In ancient and modern cultures, the moon is regarded as a
factor influencing human fate and health. The term
‘‘lunacy’’ is derived from Luna, the Roman goddess of the
moon, and from the belief that the power of the moon can
cause disorders of the mind [1,2]. The lunar phase and
the position of the moon in the zodiac is especially
claimed to be relevant for the risk of emergency opera-
tions or intraoperative complications in surgery. More
than 10% of the German population believe in a rela-
tionship between lunar phase and diseases [3]. 43% of
health professionals believe that lunar effects can affect
human individual behavior [4]. The belief that lunar
phases can influence illness may be based on Galen and
Hippocrates, but no documents exist to prove that myth.
In recent years many articles assessing the influence of
lunar phases on suicide [5–7], mental health [8], and
various accident events [9,10] have been published.
Other forms of superstition, such as signs of the zodiac
may affect human behavior in various ways. A belief in
Friday the 13th as an ill-fated day is deep-rooted in the
population [11,12]. To the best of our knowledge, there
is only one study dealing with the zodiac and its influence
on emergency cases [13].
Jochen Schuld and Jan E. Slotta contributed equally to this study.
J. Schuld J. E. Slotta O. Kollmar M. K. Schilling
S. Richter (&)
Department of General-, Visceral-, Vascular- and Paediatric
Surgery, University of Saarland, 66421 Homburg/Saar, Germany
e-mail: sven.richter@uks.eu
S. Schuld
Department of Anaesthesiology and Intensive Care Medicine,
University of Saarland, 66421 Homburg/Saar, Germany
123
World J Surg (2011) 35:1945–1949
DOI 10.1007/s00268-011-1166-8
The aim of our retrospective study over 9 years was to
evaluate if there were any statistically significant peaks of
intraoperative blood loss or frequency of emergency cases
that could be linked to lunar phenomena, Friday the 13th,
or zodiac signs.
Patients and methods
The database was comprised of all consecutive patients
admitted and undergoing general, visceral, or vascular
surgery between August 29, 2001 and August 23, 2010.
However, pediatric surgery and all other surgical special-
ities (e.g., orthopedic and trauma surgery, neurosurgery,
thoracic surgery, etc.) were excluded from the evaluation.
Collective operative records were evaluated using the
hospital information system SAP/i.s.h.med (SAP, St. Leon-
Rot, Germany). Intraoperative documentations of estimated
surgical blood loss were analyzed.
One lunar phase was defined as 29.53 days (29 days,
12 h, 44 min, 2.9 s). Friday the 13th occurs when the
thirteenth day of a month falls on a Friday. In the Grego-
rian calendar, this occurs at least once, but at most three
times a year. Any month’s thirteenth day will fall on a
Friday whenever the month starts on a Sunday. Calculation
of patient’s zodiac signs, lunar phases, and zodiac signs at
time of the operation, as well as identification of Friday the
13th, were performed using VBA scripts in Microsoft
Excel (Microsoft, Unterschleissheim, Germany) based on
the date of the operation. All values are expressed as
mean ±SEM. After proving the assumption of normality
and homogeneity of variance across groups, differences
between the groups were calculated with the Student’s t-
test. In case of non-normal distribution of data, the Mann–
Whitney U-test was performed. Comparison between
groups of categorical data was performed with Fisher’s
exact test or the chi-square test. Overall statistical signifi-
cance was set at P\0.05. Statistical analysis was per-
formed with SPSS 15 software package (SPSS, Chicago,
IL).
Results
A total of 111 lunar phases over 3,281 days were evaluated
regarding operations of 27,914 patients (16,310 men,
58.4%; 11,604 women 41.6%) with an average age of
58.8 ±0.1 (16–99) years. At least one operation was
performed at 3,153 of the 3,281 days within the observa-
tion period (96.1%). Mean estimated blood loss was
161.7 ±2.8 ml, ranging from 1 ml to 12,000 ml. In 865
procedures (3.1%), an intraoperative blood transfusion was
mandatory.
Of all the operations analyzed, 7,309 (26.2%) were
performed as emergency operations; all others were plan-
ned. Most operations were performed during waxing moon
and waning moon; 912 operations were performed during a
new moon, and 916 operations were performed during a
full moon (Table 1). Friday the 13th occurred 15 times
within the observation period, with overall 170 operations
on these days. A little more than 50% (51.8%; n=88) of
these operations were performed during the waning moon;
48.2% (n=82) were done during the waxing moon. The
‘‘worst case scenario’’—a combination of a full moon and
Friday the 13th—never occurred. Estimated blood loss and
emergency frequency did not correlate with lunar phases,
the presence of Friday the 13th (Table 2), or zodiac signs at
the time of the operations (Table 3). During the zodiac
signs of Capricorn (Dec 22–Jan 20), Aries (March 21–April
20), and Gemini (May 22–June 21), the rate of emergency
Table 1 Distribution of 27,914 operations to lunar phases and
patient’s characteristics from August 29 2001 to August 23 2010
Lunar phase nPercentage Age, years
Waning moon 13,019 46.6 58.8 ±0.1
New moon 912 3.3 58.6 ±0.5
Full moon 916 3.3 58.6 ±0.5
Waxing moon 13,067 46.8 58.6 ±0.1
Overall 27,914 100.0 58.8 ±0.1
Table 2 Emergency frequency and estimated blood loss in relation to
lunar phases and Friday the 13th
Time
point or
lunation
phase
Emergency
rate (%)
Chi
square
Pvalue Estimated
blood
loss, ml
Pvalue
Friday
the
13th
20.0 3.384 0.069 203.0 ±34.8 0.245
Normal
day
26.2 161.5 ±2.8
Friday
the
13th
20.0 0.955 0.356 203.0 ±34.8 0.079
Every
other
Friday
23.2 148.8 ±5.6
Waning
moon
26.5 2.115 0.549 160.6 ±4.0 0.676
New
moon
25.8 151.98 ±13.6
Full
moon
27.4 149.69 ±15.4
Waxing
moon
25.8 164.40 ±4.16
1946 World J Surg (2011) 35:1945–1949
123
operations significantly differed from the mean emergency
rate during the rest of the evaluation period, but whereas
estimated blood loss was comparable (Table 3). A total of
128 severe vascular (0.5 % overall) cases and 448 (1.7%
overall) severe gastrointestinal emergency cases were
found with a peak for perforated aortic aneurysms in the
zodiac sign Aries (0.7%) and a peak for gastrointestinal
perforations in Capricorn and Scorpio (2.1% each); how-
ever, neither reached statistical significance. The distribu-
tion of both entities was independent of lunar phases and
zodiac signs, as shown in Tables 4and 5.
Discussion
Moon and lunar cycles played an important role in all
ancient human civilizations, the earliest reports dating to
Sumerian and Egyptian high cultures [14]. The idea that
stars and planets may influence human health and behavior
can be traced to at least Roman times [15]. Research
suggests that a high proportion of health professionals
continue to hold this belief [4]. The fear of Friday the 13th
is called Paraskavedekatriaphobia and was first mentioned
by Coriat in 1911 [16]. A number of publications sup-
porting the hypothesis of a lunar influence [17], Friday 13th
[11,18,19], and zodiac signs alternate with a larger
number of publications rejecting any such correlation [3,8,
10,20–22]. When analyzing mentally ill people, only the
Table 5 Association between zodiac signs and operations for gas-
trointestinal perforation (P=0.398) and operations for perforated
aortic aneurysm (P=0.562)
Zodiac sign Gastrointestinal
perforation
Perforated aortic
aneurysm
Pisces 1.3%
30/2,347
0.5%
12/2,347
Virgo 1.9%
43/2,307
0.3%
8/2,307
Cancer 1.6%
42/2,572
0.5%
13/2,572
Leo 2.0%
47/2,363
0.4%
10/2,363
Sagittarius 1.3%
30/2,313
0.6%
14/2,313
Scorpion 2.1%
51/2,461
0.5%
12/2,461
Capricorn 2.1%
39/1,877
0.6%
11/1,877
Taurus 2.0%
46/2,307
0.3%
6/2,307
Libra 1.5%
36/2,333
0.6%
13/2,333
Aquarius 1.8%
42/2,399
0.3%
8/2,399
Aries 1.9%
41/2,134
0.7%
14/2,134
Gemini 1.6%
41/2,501
0.3%
7/2,501
Table 4 Correlation between lunar phases and operations for gas-
trointestinal perforation (v
2
=1.179, P=0.758) and lunar phases
and operations for perforated aortic aneurysm (v
2
=2.231,
P=0.526)
Lunar phase Gastrointestinal
perforation
Perforated aortic
aneurysm
Waning moon 1.7%
225/13,019
0.4%
57/13,019
New moon 1.4%
13/912
0.2%
2/912
Full moon 2.1%
19/916
0.3%
3/916
Waxing moon 1.8%
231/13,067
0.5%
66/13,067
Table 3 Influence of zodiac signs on emergency operations and
estimated intraoperative blood loss
Zodiac sign Emergency rate Estimated blood loss, ml
Capricorn 32.5%
610/1,877
156.3 ±9.4
Aries 29.1%
621/2,134
168.0 ±9.3
Gemini 28.3%
708/2,501
158.5 ±9.3
Leo 26.6%
629/2,363
154.1 ±9.5
Taurus 26.5%
612/2,307
149.9 ±8.7
Cancer 26.3%
676/2,572
181.1 ±10.8
Scorpio 25.5%
628/2,461
161.7 ±9.1
Libra 25.3%
590/2,333
163.4 ±9.6
Sagittarius 24.8%
574/2,313
144.6 ±9.4
Pisces 24.1%
566/2,347
173.3 ±10.3
Virgo 24.1%
555/2,307
162.2 ±9.9
Aquarius 22.5%
540/2,399
164.8 ±9.7
World J Surg (2011) 35:1945–1949 1947
123
mental health of patients with schizophrenia has been
shown to be affected by moon phases [8]. Kredel et al.
report that postoperative nausea and vomiting are not
influenced by lunar cycles [20]. The first medical doctor
scientifically dealing with the problem of bleeding and
lunar phases was Andrews in 1960 [18]. In his original
publication, only a pseudo-coincidence of postoperative
bleeding complications after tonsillectomy was found [23].
The myth that moon phases influence long term follow-up
in oncological surgery was broken by May et al. [22], as
well as by Kuehnl et al. [21]. As there are no studies
evaluating moon effects, zodiac signs, or Friday the 13th
on intraoperative blood loss and emergency frequency, we
have evaluated almost 28,000 patient records in 111 lunar
cycles representing the biggest cohort dealing with this
question to our knowledge. When analyzing big cohorts for
cyclical aspects or trends—as given by moon phases and
zodiac signs—the number of investigated cycles is more
important than the overall number of investigated subjects.
The results of our study are in line with most previously
published studies dealing with the influence of folk belief
on surgical complications [3,23,24]. The fact that emer-
gency cases are more frequent during the zodiac signs of
Capricorn, Aries, and Gemini is easy to explain because the
religious Christian holidays (Christmas, Easter, and Whit-
sun) cumulate in these periods. By definition, all operations
performed on holidays were classified as emergencies. It is
important to note that the emergency cases investigated in
our study are not influenced by human behavior as
described in previous studies [11,19]. This potential bias is
unmistakably excluded in our discipline, as emergency
cases in general, visceral, and vascular surgical occur only
due to internal patient characteristics and therefore repre-
sent unpredictable, stochastic events.
Admittedly, some shortcomings of the present study
have to be faced. First, one could argue that there may be
some systematic error as the data represent only a single-
center experience with 3,000 patients treated per year.
However, our database comprises all patients treated in
general, visceral, and vascular surgery at a tertiary referral
centre for 1 million people. Second, our study is limited
insofar that the statistical power for both perforated aortic
aneurysm and gastrointestinal perforation is 0.125 and
0.203, respectively. To reach a desired power level of 0.8,
this study would require 135,025 perforated aortic aneu-
rysm patients and 255,395 gastrointestinal perforation
patients. Such large cohorts can only be evaluated in
population-based registries [25,26] but are not available
for surgical patients. To our knowledge, however, no study
dealing with the problem of superstition in medicine to date
has provided a detailed power and sample size calculation.
Third, recent studies dealing with the influence of the full
moon on medical emergency cases may face a large degree
of beta error because of small patient cohorts and rare
events [3,17,21,24,27]. To overcome the problem of
analyzing rare events in a cyclical context within a limited
number of patients, some of the recent studies have not
clearly defined the event of ‘‘full moon’’ or allocated this
event to a time period of several days [22,27]. Fourth, the
estimation of intraoperative blood loss is strongly biased by
surgeons’ tendency to underestimate blood loss systemat-
ically [28,29]. At this point, the single-center approach
may provide an advantage by reporting standardized
measurements and correct documentation of intraoperative
blood loss. A final criticism of the present study may be
that 128 days are lacking in our investigation because
neither emergency cases nor elective surgeries were per-
formed on those days. However, the proportion of lunar
phases and zodiac signs in these lacking days was com-
parable to the rest, so that no statistical bias should occur.
Looking back, numerous studies have dealt with myths
and popular belief in modern medicine. Although most
publications deny any influence of superstition, some
studies still support this view [17,30], and evidence is
weak. Therefore, further research in the context of rare
unpredictable events—especially when dealing with cyclic
phenomena (e.g., moon phases, weather conditions, sea-
sons)—will require large databases of patients, which can
be recruited preferably from multicentric settings. In view
of the fact that trauma- and orthopedic surgery have been
excluded from the data set reported here, we finally want to
state that the impact of lunar phases and other influences on
human behavior that would have an impact on risk taking
and injury or trauma cannot be answered by the present
study.
Taken together, our results support the evidence that
operation scheduling according to lunar phases and zodiac
signs, as well as avoiding Friday the 13th for elective
surgical procedures is nothing more than medical nonsense.
Consequently, on the one hand, there is no reason for
patients to fear adverse health effects by scheduling oper-
ations during full moon phases or on Friday the 13th. On
the other hand there is no reason for health professionals in
emergency services to avoid Friday the 13th or full moon
phases on the staff roster. Finally, we want to highlight that
the current investigation is more than a humorous analysis
of a popular belief. The possible effect of these factors on
operation scheduling would be quite relevant for personal
and resource planning.
Conclusions
The hypothesis that lunar phases, zodiac signs, and Friday
the 13th influence blood loss and emergency operations is
not valid and only myth. So far, however, studies with
1948 World J Surg (2011) 35:1945–1949
123
adequate power and sample size calculation rejecting any
association between superstition and medicine are under-
represented in the medical literature.
Acknowledgments The authors greatly appreciate the help of Ms.
Catherine Black, University of Manchester, for proofreading and
substantive contributions concerning language and style of the
manuscript.
Conflict of interest None.
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