Well, Not Really

Two siblings being born on the same day in different years was unlikely enough. But when Kim MacKriell had a third child delivered on the same day, she beat odds of more than 130,000 to one.

Ruby MacKriell was born last month on January 29. Her brother, Robin, was born on January 29, 1994, and her sister, Rebecca, on January 29, 1996.

According to statisticians at the University of Cambridge and the London School of Economics, the chances of this happening are 7.5 in 1 million.

Depends how often you shag really. If it\’s a special event every April 29th then those odds really do shorten quite a lot.

7 comments on “Well, Not Really

  1. I like the way they felt they needed to consult statisticians at two universities to work this out.

    Odds of two siblings born on same day: 1/365. Odds of three siblings born on same day: 1/(365^2)

    =1/133225 or, in a slightly weird way of expressing it, 7.5 in one million.

    If only these journalists consulted their children doing GCSE maths, they could avoid bothering the university statisticians.

  2. This is a good week to remember that it should be 1/(365.25^2) = 1/133407.5625.

    The 7.5 in a million number is useful for realising how unusual this isn’t – for every million mothers with three children (maybe five million in the uk?) there are 7.5 examples of this or around 38 families.
    Now, if she’d put a bet on it beforehand, that would have been interesting!

  3. ‘Now, if she’d put a bet on it beforehand, that would have been interesting!’

    If I were the bookmaker, I would want to know if they were Catholics……

  4. It also assumes its a random event (and one predicted if you’re going to talk about ‘beating the odds’), which even if they only tried for ‘sometimes after Christmas’ reduces the odds rather a lot.

    Still nice story so don’t want to sound too grumpy.

  5. Journalists always fail to understand the Law of Large Numbers. Even if we assume that the odds really are 1 in 133225 for any given triplet of siblings, when you consider that millions of children are born every year, the likelihood of this happening to some family at some point are high. Or as Terry Pratchett would put it, million to one shots happen nine times out of ten.

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