Friday the 13th is considered an unlucky day in western superstition. Theories on why it has become known as unlucky range from there being 13 people present at the last supper according to the Bible to Loki being the secret 13th secret guest at a dinner party for the Norse gods before generally causing all kinds of chaos.
While it would be easy to dismiss such claims (just because someone says "Tuesday the 20th is filled with whimsy" doesn't mean you have to investigate it), is there any truth to the idea that the day is unlucky, or statistics to back it up?
Well, there have been a few attempts to look into it. One team, interested to see if they could measure how superstitious people are and whether this affected their behavior, examined traffic flow and accident data. The idea was that they could "make reasonable inferences as to just how superstitious people are by examining their behaviour - for example, are people less likely to drive and shop on Friday the 13th?"
The study, published in the BMJ in 1993, found some tentative evidence that people may alter their behavior on Friday the 13th.
"Fewer people seem prepared to drive on motorways on Friday the 13th. About 1.4% of the population may be so affected," the team wrote.
"Analysis of data comparing, for example, Friday the 5th with Friday the 12th would rule out other unrecognised reasons for weekly changes in driving pattems."
According to the study, admissions to hospital from transport accidents rise on Friday the 13th despite fewer cars on the road. Though they note that the number of accidents studied was too small to allow meaningful analysis, suggesting a bigger study would be necessary to support or refute, they add that "the risk of a transport accident on Friday the 13th may be increased by 52%".
For this, they offer the possibilities that larger studies will not find the same increase, there is some unrecognized factor affecting road traffic accidents, it is some quirk of how accidents are recorded on Friday the 13th, Friday the 13th is actually unlucky, or people who are superstitious are making behavioral changes on that day which makes their driving unsafe.
"Are people's perceptions and beliefs self fulfilling-if you believe something strongly enough will it in fact happen to you?" they write in the discussion. "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."
While an intriguing thought, other studies looking at admissions to the emergency department have found no increase on the day.
"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," one larger study looking at emergency departments in the US concluded. "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." Except, of course, for those extra penetrating traumas.
Other studies, such as one conducted by the Dutch Centre for Insurance Statistics, have found that roads are slightly safer on Friday 13th.
“I find it hard to believe that it is because people are preventatively more careful or just stay home," statistician for the center Alex Hoen reportedly told the Verzekerd insurance magazine at the time, "but statistically speaking, driving is a little bit safer on Friday 13th."
So, in summary: there is no real, conclusive evidence that there is an increase in accidents on Friday the 13th, with several showing the opposite. Even those that do show a difference explain it with behavioral changes by the superstitious.
Furthermore, people who continue to believe that Friday the 13th is unlucky are probably engaging in a form of confirmation bias. You may injure yourself three times a month, or else have some other form of bad luck. This could happen on a Sunday the 1st, Friday the 13th, or any other day of the month, but given that Friday the 13th is supposed to be unlucky, which incident do you – a very superstitious person – think you are going to remember?
But maybe be on the lookout for penetrating trauma, just to be on the safe side.