Why the number 13 tram isn’t that unlucky
Wednesday, October 13th, 2010 | Thoughts
Last month at Humanist Community, Gijsbert presented a news story about the number 13 tram in one city which had an exceptionally high accident rate and had therefore been withdrawn from service because with it being the number 13, it was clearly cursed.
While most of my blog’s readership will already have explained to themselves why this is nonsense, I though I would attempt to to clarify the situation for anyone who might actually take such an example as evidence that the number 13 is genuinely unlucky.
Lets start with the probably. I’m going to guess that there are somewhere in the region of 100 cities with tram networks in them. This may or may not be accurate though there is technically no reason why you should limit it to trams, you could also include buses for example and create a much larger sample which works even better for example.
Now lets say that on average there are 20 routes on each network. This could be off again but I’m basing this on the idea that there are probably less tram routes than there are bus routes and this a little on the low side for Leeds bus routes but then we’re not a huge city on a world scale.
With every network, statistically one of those routes must be the most accident prone. With 20 routes, one of them being 13 (maybe some places avoid having a route 13 – but again, Leeds doesn’t, so I’m going to go with that), that means there is a 1/20 chance of the most accident prone route being route 13. That is 5%. 5% of the 100 tram networks in the world means that statistically, you would expect the route 13 to be the most accident prone in 5 different cities in the world, just by chance. Equally in the same amount of cities, the number 7 or the number 3, or any number, will be the most accident prone route.
Add to that the fact that some people are superstitious and even though most of us know that 13 genuinely isn’t unlucky, you may occasionally get say a tram driver that is superstitious and becomes nervous when driving route 13 because he believes it is “cursed.” Thanks to the nocebo effect (the opposite of the placebo effect) the route then becomes a self fulfilling prophesy.
But even if we discount that and say that all such superstitious tram drivers simply refuse to drive the route 13 tram, we are still left with five places in the world which the route 13 tram is the most accident prone simply by chance – of which of course there will be different levels of accidents, most non-exceptional, some will be quite highly though, that’s just how random probably is.
So, we now have a really unlucky tram. It’s one of the five places where route 13 is the most accident prone simply by chance, and it’s the worst one of those. A journalist notices this, presumably working at The Sun, and decides to write a story on it.
But of course, no one thinks to write a story on the city which has the tram network where the route 7tram is the most accident prone simply by chance and happens to the the worst of the five cities in which this is the case – it only makes the news because someone comes along and makes the non-existent connection between this being the city which is one of the five cities in which the route 13 tram has the highest accident rate and this one happens to be the worst and the superstitious belief that the number 13 is unlucky.
When in fact what would be weird is if out of all the tram networks in the world, there wasn’t a single one where the route 13 tram wasn’t in at least one instance the most accident prone route on that tram network.
Last month at Humanist Community, Gijsbert presented a news story about the number 13 tram in one city which had an exceptionally high accident rate and had therefore been withdrawn from service because with it being the number 13, it was clearly cursed.
While most of my blog’s readership will already have explained to themselves why this is nonsense, I though I would attempt to to clarify the situation for anyone who might actually take such an example as evidence that the number 13 is genuinely unlucky.
Lets start with the probably. I’m going to guess that there are somewhere in the region of 100 cities with tram networks in them. This may or may not be accurate though there is technically no reason why you should limit it to trams, you could also include buses for example and create a much larger sample which works even better for example.
Now lets say that on average there are 20 routes on each network. This could be off again but I’m basing this on the idea that there are probably less tram routes than there are bus routes and this a little on the low side for Leeds bus routes but then we’re not a huge city on a world scale.
With every network, statistically one of those routes must be the most accident prone. With 20 routes, one of them being 13 (maybe some places avoid having a route 13 – but again, Leeds doesn’t, so I’m going to go with that), that means there is a 1/20 chance of the most accident prone route being route 13. That is 5%. 5% of the 100 tram networks in the world means that statistically, you would expect the route 13 to be the most accident prone in 5 different cities in the world, just by chance. Equally in the same amount of cities, the number 7 or the number 3, or any number, will be the most accident prone route.
Add to that the fact that some people are superstitious and even though most of us know that 13 genuinely isn’t unlucky, you may occasionally get say a tram driver that is superstitious and becomes nervous when driving route 13 because he believes it is “cursed.” Thanks to the nocebo effect (the opposite of the placebo effect) the route then becomes a self fulfilling prophesy.
But even if we discount that and say that all such superstitious tram drivers simply refuse to drive the route 13 tram, we are still left with five places in the world which the route 13 tram is the most accident prone simply by chance – of which of course there will be different levels of accidents, most non-exceptional, some will be quite highly though, that’s just how random probably is.
So, we now have a really unlucky tram. It’s one of the five places where route 13 is the most accident prone simply by chance, and it’s the worst one of those. A journalist notices this, presumably working at The Sun, and decides to write a story on it.
But of course, no one thinks to write a story on the city which has the tram network where the route 7tram is the most accident prone simply by chance and happens to the the worst of the five cities in which this is the case – it only makes the news because someone comes along and makes the non-existent connection between this being the city which is one of the five cities in which the route 13 tram has the highest accident rate and this one happens to be the worst and the superstitious belief that the number 13 is unlucky.
When in fact what would be weird is if out of all the tram networks in the world, there wasn’t a single one where the route 13 tram wasn’t in at least one instance the most accident prone route on that tram network.