Jeffrey Rosenthal was a young professor at the University of Toronto when he discovered he was born on a Friday - though not just any Friday.
"Everyone knows their date of birth and mine is Oct. 13," says Rosenthal, a professor of probability and statistical computing in the Faculty of Arts & Science's department of statistical sciences . "But it wasn't until I wrote my own calendar computer program and went all the way back to my date of birth with it that I discovered I was born on Friday the 13th."
Rosenthal recently published a paper in the journal Chance with co-author Jennifer Dmetrichuk - an assistant professor in the department of laboratory medicine and pathobiology at the Temerty Faculty of Medicine and a forensic pathologist and regional supervising coroner in Toronto - that explores the widely held notion that bad events are more likely to occur on Friday the 13th, a fear known as paraskevidekatriaphobia or friggatriskaidekaphobia. They also looked at the effect of full moons, Halloween and times of year.
"Scientific literacy is important to me," says Rosenthal, who is the author of Struck by Lightning: The Curious World of Probabilities and Knock on Wood , both of which explore probability and luck. "I'm trying to convince people how important it is to understand how the world works and that we shouldn't make up superstitions.
"That and the fact I was born on Friday the 13th made this study more personal for me than most."
U of T Faculty of Arts & Science writer Chris Sasaki recently spoke to Rosenthal about what he and Dmetrichuk learned.
Where did the superstitions about Friday the 13th originate?
It's hard to pin down but there've been many inauspicious events in history associated with that day. For example, there were 13 people at the Last Supper and one of them, Judas, betrayed Jesus. On Friday, Oct. 13, 1307, King Philip IV of France infamously arrested many members of the Knights Templar which eventually led to the end of the order. There are many other events and associations throughout history that have reinforced the belief. There's also the idea that 13 is the first "unfamiliar" number, the smallest number we can't easily picture in our heads.
Is there anything else behind our embrace of superstitions?
I think one of the reasons they arise is because we as humans like to believe there are reasons things happen. For example, with the full moon, people had this sense there was some power from above - gods or celestial objects - that had an influence on us. They thought that when bad things happened, it wasn't just random bad luck. It was because of the full moon or because it was Friday the 13th; or when good things happen, it was because of your astrological sign.
People want to believe these things - that there's some force which gives meaning to what goes on. And once these superstitions begin, they tend to snowball because people look for confirmation of their beliefs.
Is this confirmation bias?
Yes. Confirmation bias is when you have a belief and then you look for evidence that it's real. So, if something bad happens on Friday the 13th, you notice and remember it and it confirms the superstition whereas if something bad happens on any other day, you don't remember it. For example, the Apollo 13 spacecraft suffered an explosion on April 13, 1970 - and even though it was a Monday and not a Friday, it confirmed the belief for many.
And confirmation bias doesn't just come up in superstition. For example, if you hate a certain politician, then any bad thing they do is proof to you they're really a bad politician, right? Whereas if they do something good, you tend to ignore it.
How did you conduct your study and what did you find?
We looked at data for all the unexpected deaths in Ontario for the 15-year period from 2009 to 2023. So, for example, deaths from homicide, accidents and unexpected natural deaths. We thought that's a pretty good measure of something bad happening or bad luck.
We had data for over 250,000 deaths and we looked at how many happened on Friday the 13th. We compared them to the overall rate of unexpected deaths on days other than Friday the 13th and we found - with apologies to the millions of superstitious people around the world - there really wasn't any difference. In other words, Friday the 13th isn't more dangerous than any other day in terms of suspicious or unexpected deaths. In fact, the rate was a tiny bit less than the overall rate. We also didn't find any increase for full moons or Halloween.
So, this is pretty good scientific proof that all those fears are really not justified.
Were there any correlations between deaths and other dates or times of the year?
Yes. We checked the Christmas holiday period and deaths by months and found a fairly pronounced effect, actually. We found what others have seen - that more people die unexpectedly in the winter than in the summer from heart attacks and strokes. And one obvious reason for this is that in the winter, people participate in more strenuous activities like shovelling snow and this can put a strain on their cardiovascular system. It doesn't have anything to do with superstition or bad luck.
Do you do anything that might be even slightly superstitious?
People ask me that all the time. For the most part, no. But that doesn't mean I don't find myself thinking that way a little bit. For example, before the 2016 American presidential election, I made a bet with a political science professor that Trump would win. We agreed on two-to-one odds, so he put up $2 to my $1. And of course, Hillary Clinton lost and Trump won and I got my $2.
But then I got this weird feeling that it was my fault that Trump was elected - that it was somehow because I made this bet. Of course, that's absurd. But I found myself thinking that. And that just shows the real human need to connect events like this: a bet and an election outcome. We want to think that what we do has some influence even though, as in this case, it didn't have any influence at all.
For me, I'm trying to figure out the way the world really works. Understanding the science - that's what's interesting. As soon as you start believing in superstitions that don't have a scientific basis, you're abandoning that truth.
Besides, I was born on Friday the 13th and I've had a pretty good life - so that shows it's not really a bad thing.
