Without evidence of benefit, an intervention should not be presumed to be beneficial or safe.

- Rogue Medic

The Magical Nonsense of Friday the 13th


Today we celebrate the fears of those who do not understand that magic does not affect reality. Our fears of magic can affect reality, when we act on those fears. Why should a special day cause more problems than a boring day? Many people believe in magic powers as being more than just the fictional entertainment we see in novels and movies.

Here is another study of the effects of Friday the 13th on emergency medicine/EMS that I have not written about. It is no surprise that they did not find what is not there – an influence of this magic date on the type or volume of patients in the emergency department.

Although the fear of Friday the 13th may exist, there is no worry that an increase in volume occurs on Friday the 13th compared with the other days studies. Of 13 different conditions evaluated, only penetrating traumas were seen more often on Friday the 13th. For those providers who work in the ED, working on Friday the 13th should not be any different than any other day.


When measuring of a large number of variables, it is expected that one, or more, will appear to be statistically significant. This is why the p value of outcomes should be adjusted when there are multiple outcomes being measured. The p value is just a measure of how likely it is that the result occurred by chance (and thus meaningless), so the more chances, the more likely that the meaningless is considered significant.

Fear of Friday the 13th is mistakenly attributing some magical power to a day, to a number, to the calendar, and/or to some other variation of belief in the magic of numbers.

Numbers are important and can provide us with useful information about the risks in our lives. The risks we take confidently, cautiously, or those we don’t take. Often our decisions about risk are based on faulty information, such as the fear of a date. Mathematical literacy is necessary to understand the ways that we can use numbers to obtain valid information. John Allen Paulos created the term innumeracy to describe our lack of literacy in the language of numbers. He explained this in 1988 in his book Innumeracy: Mathematical Illiteracy and its Consequences.[2]

Innumeracy cover


Oh! But what about Lies, damned lies, and statistics?

Doesn’t using math make it easier for people to lie to us?

No. Ignorance of math makes it easier for people to lie to us with math.

People do not often lie with numbers. People lie with words. Maybe they lie with the salesman smile. Maybe they lie with the fear monger frown. Maybe they lie unintentionally, because they don’t know what they are talking about. They lie with words. Our ignorance of logic, not our understanding of math, is what allows us to fall victim to most lies.

Today is another Friday that is no more exciting than any other Friday.

Luck works in our favor when we are prepared for the results of our actions, but that is not the kind of luck many people want to understand.

Happy Friday the 13th – New and Improved with Space Debris – Fri, 13 Nov 2015

Friday the 13th and full-moon – the ‘worst case scenario’ or only superstition? – Fri, 13 Jun 2014

Blue Moon 2012 – Except parts of Oceanea – Fri, 31 Aug 2012

2009’s Top Threat To Science In Medicine – Fri, 01 Jan 2010

T G I Friday the 13th – Fri, 13 Nov 2009

Happy Equinox! – Thu, 20 Mar 2008


[1] Answering the myth: use of emergency services on Friday the 13th.
Lo BM, Visintainer CM, Best HA, Beydoun HA.
Am J Emerg Med. 2012 Jul;30(6):886-9. doi: 10.1016/j.ajem.2011.06.008. Epub 2011 Aug 19.
PMID: 21855260

[2] Innumeracy: Mathematical Illiteracy and its Consequences
Page on Wikipedia



  1. Thanks Pope Greg and your calendar, you ruined it all! 😉

  2. Was the penetrating trauma inflicted with Freddy claws or a Jason machete?

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