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Popular Belief Meets Surgical Reality: Impact of Lunar Phases, Friday the 13th and Zodiac Signs on Emergency Operations and Intraoperative Blood Loss



The influence of superstition, moon calendars, 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.


We analyzed the extent to which moon phases, zodiac signs, and Friday the 13th influence blood loss, emergency frequency, and intestinal perforations by evaluating 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.


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.


Scientific analysis of our data does not support the belief that moon phases, zodiac signs, or Friday 13th influence surgical blood loss and emergency frequency. Our data indicate that such beliefs are myths far beyond reality.

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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.

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Correspondence to Sven Richter.

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Jochen Schuld and Jan E. Slotta contributed equally to this study.

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Schuld, J., Slotta, J.E., Schuld, S. et al. Popular Belief Meets Surgical Reality: Impact of Lunar Phases, Friday the 13th and Zodiac Signs on Emergency Operations and Intraoperative Blood Loss. World J Surg 35, 1945–1949 (2011).

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  • Estimate Blood Loss
  • Full Moon
  • Emergency Case
  • Popular Belief
  • Gastrointestinal Perforation