A young mother has given birth to her second Christmas Day baby – defying odds of more than 130,000 to one.

Those odds would be right if the two births were truly independent events. But what if the 25 th March is his birthday? Or hers? Or some other celebration that makes a jump more likely? Possibly, even just spring friskiness?

What’s most concerning is that it’s a bookie who can’t seem to sort out the odds, not even a scientist who could be expected to mangle the numbers, perhaps even deliberately. Maybe we should all go and take him to the cleaners.

It’s not at all a long shot at 1/365 to give birth on Christmas day (or any other day). That’s also important as we can do the same trick with Easter, new year, Mohammed’s birthday, the fourth full moon of the year and so on. Also the events really can’t be independent as you know the result of one before the other. So it would be pretty easy to manipulate the second one. That said, that about 1/130,000 mothers have successive children on Xmas day sounds about right. The same of course applies to any other day (except February 29), so two births on any same day will happen in about 1 in 350 families.

If the events are independent. Which given a 9-month gestation and the usual time-to-resumption-of-shagging after birth, they are not.

My birthday is 14/08.

My older brother’s is 02/04

My younger brother’s is 17/09.

The odds of that is about one in 48 million.

How special are we?

I think this is excessive nitpicking. Unless you presume the couple were specifically trying for a Christmas baby, it’s not unreasonable to presume effectively random birthdays. I was born in February. My sister was born in September. Most families have birthdays spaced around the year. When you factor in that the human reproductive system seems to have specifically evolved to have a low likelihood of pregnancy from any particular copulation as well, so it is very hard for couples to plan dates of birth even if they want to, the statistics are adequate enough. The probability of two random births on the same specific day is 1/(365^2). The probability of two births on the same arbitrary day, as JamesV says, is 1/365.

About 800,000 babies are born in the UK each year, so it’s not surprising if some of them defy odds of 130,000 to 1.

However, I suspect that fewer than 1 in 365 babies are born on Christmas day, because obstetricians will tend to avoid it, both by the timing of elective Caesareans and by intervening to bring forward labour in the event of minor complications in very late pregnancy.

I was born in April 1977, 9 months after the great heatwave of July 1976 when my parents were living in a caravan while the house was being redone. As it happened, there were a cluster of us in the school year born around mid-April 1977. It’s not too difficult to figure out why.

As someone born early September, I always put it down to a surplus of alcohol, New Year’s Eve.

Given a random selection of 97 people and assuming that birth days are also random, standard probability results in better than 99% chance that 2 of them will share a birthday.

Even with 23 people, it’s a better than 50% chance.

(look up birthday paradox)

And it was a bookie came up with 130,000/1? Where’s his shop?

This mother has had two children, not 23. And baby Jesus has got the same birthday too, allegedly.

Sadly, you none of you remember Today when it was run by Jack de Manio and there was a super interviewer called Monty Modlin.

At one stage Monty interviewed a lady who had several children all born on the same day. Closing question – “Do you think you will have any more children born on the same day?”

“We didn’t celebrate my husband’s birthday this year.”

I suspect that my birthday is related to my father’s return from The War.

From memory, the probability of someone having two children with the same birthday (excluding twins) is only around 1 in 1000.

On that basis, I too would like the number of bookie who came up with odds of 130,000 to 1.

The probability of two birthdays the same is 1/365. The probability of two birthdays on the same specific day is 1/365^2 which is 1/133,225.

“The probability of two birthdays the same is 1/365.” Only if you assume that the date of the second one is statistically independent of the first. See anecdote above #9 (Dizzy Ringo).

It’s a reasonable assumption, in the absence of other evidence.

Ian,

Yes, I’d give you that, if there weren’t an abundance of other evidence. Human sexual behaviour isn’t as random as the Daily Hate likes to portray it, for a start.

A wee while ago, there was a big thing up here in the soggy north, about Christmas babies. Much fuss and many freebies from the baby-pandering industry. One couple won it three times (not in a row, iirc, but I may be wrong.)

I do remember they were Muslim.