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

- Rogue Medic

Is Friday the 13th bad for your health


Also posted over at Paramedicine 101 and at Research Blogging.

Go check out the rest of the excellent material at these sites.

Somebody actually studied the health effects of Friday the 13th, or tried to.


Superstitions affect behaviour in all cultures in all parts of the world in some form or other. Most work, however, seems to have focused on the effects of supernatural beliefs in developing countries.1-6 Perhaps there is a subconscious perception that people in the West are too sophisticated to be influenced by such trifles.[1]

We’re anthropologists studying the superstitions of the native population in Southern England. Don’t mind us. Just go about your ordinary superstitious behaviors.

Why these have been chosen as unlucky if occurring on a Friday is not clear. Other superstitions around Friday have more apparent origins. For example, laundry should never be washed on a Friday. A Yorkshire legend has it that as Christ was walking to Calvary a woman washing outside her house derisively waved a wet garment at his face, whereupon he cursed her and all who should in future wash on that day.[1]

This is reminiscent of some of the old medics’ tales in EMS that are cited as the basis for otherwise baseless nonsense, such as – If you don’t give anti-nausea medication with morphine, then the patient will vomit. A small percentage of patients receiving morphine will develop nausea, but only some of that small percentage of patients will end up vomiting.

Few people are married on the 13th, and Friday the 13th, particularly if it falls in May, is regarded with extreme foreboding.[1]

Maybe people are just goofier in May.

Happy Friday May 13th! 🙄

Examination of the weather patterns for the south east did not show different weather patterns for the two Fridays. (The weather does not seemto be any more unlucky.)[1]

Doesn’t that depend on what is unlucky for the weather?

How do we know that the weather doesn’t consider a storm to be a lucky occurrence?

There were 1.4% fewer vehicles on the southern section ofthe M25 on Friday the 13th-even if each vehicle had only one occupant this could mean at least 1.4% of the population are sufficiently superstitious to alter their behaviour and refrain from driving on motorways on Friday the 13th.[1]

A whole 1.4% difference?

How large is their error rate?

If their error bars are +/- 1% for their daily numbers the number of people on the roads could actually be higher on a typical Friday the 13th.


Although the numbers of admissions from accidents are too small to allow meaningful analysis, there seem to be more injuries from transport accidents on Friday the 13th-despite there being fewer vehicles on the road. But there are several caveats in any calculation from our data of a risk ratio for suffering a transport accident on Friday the 13th: such accidents could involve any form of transport, though motor vehicles comprise the vast majority; the accidents we recorded happened anywhere in Britain to residents of South West Thames region; the information on traffic flows refers specifically to numbers of vehicles on the southern section ofthe M25. That said, our data yield a risk ratio of 1.52-that is, the risk of a transport accident on Friday the 13th maybe increased by 52%.[1]

There is a problem with the wording of this. They did not collect data on transport accident rates. They collected data on admissions from admissions coded as transport accidents.

To address the second question we looked at the number of admissions for accidents and poisoning in South WestThames region and at what we agreed were the particularly unlucky accidents that could occur.[1]

Without more information about variables that might not be apparent, it seems that very little was done to assess or control for variables.

Is Friday the 13th bad for your health - Table 4

Is an animal-related accident 3 times more likely on a Friday the 13th?

Is an accident of undetermined type 4 times more likely on a Friday the 13th?

And why do fewer people fall on a Friday the 13th? No. Why are fewer people admitted to the hospital for accidents caused by a fall on a Friday the 13th?

Maybe gravity is weaker on a Friday the 13th and the lack of good contact between the ground and the vehicles’ tyres leads to more transport accident admissions! 😳


There are four possible reasons for the findings: (i) chance: further work on larger samples would confirm or refute our evidence; (ii) confounding: some hitherto unrecognised factor may be related to both driving patterns and accident rates; (iii) bias: that those recording accident data may be more likely to record accidents on Friday the 13th; (iv) association: Friday the 13th is a more unlucky day. Other than the people who stay off motorways, there maybe people who are superstitious, but not enough to refrain from motorway driving. Do drivers on A, B, C, and D roads alter their behaviour, and in what way? Is the alteration-for example more wariness-a positive change making them more careful and thus reducing the chance of an accident? If so, Friday the 13th may indeed be a very unlucky day. If the change in behaviour reveals itself by increased fear and anxiety, or perhaps a sense of destiny, it may reduce concentration and increase the likelihood of an accident. Are people’s perceptions and beliefs self fulfilling-if you believe something strongly enough will it in fact happen to you? While we await the answers to these difficult questions we may just have to accept that Friday the 13th is indeed unlucky for some and it might be safer to stay at home.[1]

Perhaps the conclusion should be that the risk of a transport accident on Friday the 13th maybe increased by 52% for the neurotic.

As you can see, there are variables that can be used to justify a Friday the 13th effect, but these same variables can also be used to counter a Friday the 13th effect.

Trying to explain data that do not reach significance is a waste of time. This is like the explanations for the stock market being up/down/flat on any particular day. For a vivid example of this, the release of FOMC (Federal Open Market Committee) meeting minutes. The market may shoot up for 10 minutes, then drop dramatically below where it was when the minutes were released, then rise for the rest of the day and fall all the next day with no new major market news. At each of these points, the financial news people will usually state that the market is up/down/flat because of the FOMC minutes. The reality is that there are many variables that affect the market. Billions of shares are traded every day, but we can only guess at the reasons.

Trying to come up with a nice simple explanation for something that has many variables, not all of which are known, is a mistake. It is a narrative fallacy to pretend that we can give valid explanations for things we do not understand.

PS – This was in the BMJ Christmas issue, which customarily has more satire and whimsy than can be found the rest of the year.

Late entries – 5/13/2011 at 12:03 –
David Konig contributes his own post along these lines – 13 Superstitions In EMS.

And at EMS World is an article on our very own EMS Mythbuster, Dr. Bryan Bledsoe.


[1] Is Friday the 13th bad for your health?
Scanlon TJ, Luben RN, Scanlon FL, Singleton N.
BMJ. 1993 Dec 18-25;307(6919):1584-6.
PMID: 8292946 [PubMed – indexed for MEDLINE]

Free Full Text with link to download Free Full Text PDF from PubMed Central

Scanlon TJ, Luben RN, Scanlon FL, & Singleton N (1993). Is Friday the 13th bad for your health? BMJ (Clinical research ed.), 307 (6919), 1584-6 PMID: 8292946



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