Non-amazing twin coincidence (updated)
Stuff is reporting, in their Oddstuff section, a story about twins who will turn 11 tomorrow, 11-11-11. How odd is this?
There are about 64000 births per year in New Zealand, or about 175 per day. The rate of twin births is somewhere between 1 in 60 and 1 in 100, so on an average day, such as 11-11-00, there will be about two pairs of twins born. So we’d expect two pairs of Kiwi twins to turn 11 on 11-11-11. You might wonder what the other pair was doing.
If you read the story, though, you see it’s actually from the United States: Madison, Wisconsin. There were more than 50,000 pairs of twins born in the US in 2000, so we’d expect about 136 pairs turning 11 tomorrow.
There must be lots of community papers across the world reporting on a pair of local twins turning 11 tomorrow. The interesting question is how the Overman twins got their story on to the Associated Press wire and into 181 (and counting) newspapers around the world, and how the same mechanisms are used on stories that aren’t just harmless fluff.
Updated: Now there’s a local pair of twins, one of whom is quoted as saying “There are probably only one or two [sets of twins] in the world turning 11 on that date.”
Updated again: You’d expect there to be several sets of birthday triplets out there somewhere in the industrialized world, and one set have shown up in Windsor (Canada). Unfortunately, the story also spends a lot of time with Uri Geller, trying to get Deep Significance out of the date.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »
I think you are being a little harsh — there is no claim in the story that it is particularly unlikely. If one is going to pay attention to the numerical oddity that is the date today, you might as well pile in and find an 11 year old…
12 years ago
I did say “harmless fluff”, and if it had just been a local story I wouldn’t have bothered. Reporting on a pair of twins from halfway around the world definitely gives the impression that they are something unusual.
Today there is a local example, but also a definite assertion that it’s unusual. I’m not blaming the kid — while he should be able to do the arithmetic, there’s no reason he should have to do it on his birthday — but it’s a definite example of basic probabilities in the media.
12 years ago
The calculation will be most accurate if it’s based on the birthrate 11 years ago (which perhaps yours was).
12 years ago
I couldn’t find the birthrate 11 years ago for NZ. I did find that the lowest number of births in the past decade was about 55000, so it was more than that in 2000.
For the US the data are even better than that: there is information on the actual number of twins born in the year 2000: about 118,000.
12 years ago
Assuming I carried out that tricky “division by two” operation correctly, there were 857 pairs of twins (both live) born in 2000 in New Zealand.
The table you want on Infoshare is ‘Live births, stillbirths by single/multiple combinations (Annual-Dec)’ under ‘Population’ -> ‘Births – VSB’.
12 years ago
Thanks, that’s useful. The back-of-envelope calculation wasn’t too far off, I’m glad to see.
12 years ago