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AIBU?

Share your dilemmas and get honest opinions from other Mumsnetters.

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Original poster

3 kids - gender stats probability

133 replies

Blackcoffeeandbiscuits · 08/12/2023 13:29

I read in a few threads that the 3rd kid is most likely to be whatever the 2nd was.

So, if you had G-B then the third will be B
If you had B-G then another G is to follow
If you had G-G chances are that the third will be G, same as if you got B-B you will most likely get another B.

I know in theory each time the chances are 50-50 but this is what research/stats have said.

Is it true though? Let's find out!

AIBU - You have GBG or BGB or BBG or GGB
AINBU - You have GBB or BGG or BBB or GGG

OP posts:

Ladylalaboo1 · 09/12/2023 22:26

I have GGG and I'm the G in my family of GBB , and then my mum is the eldest G in her family of BGG and then my dad is the eldest B of his family of BGG so definitely seems to follow the pattern here!

namechangedforthisone35 · 09/12/2023 07:23

GGB

Quinque · 09/12/2023 04:26

GBG

4catsaremylife · 09/12/2023 01:35

BGG

Georgeandzippyzoo · 09/12/2023 01:31

My parents
GBG
Brother
BGG
Cousins
GGB
BBG
Friends
GGB
BGB

wossgoinon · 09/12/2023 01:24

I have had

BBGB

my paternal gran

BBBBBBG

my maternal gran

BGGG

Rewis · 09/12/2023 01:18

Thinking my immediate friend and family with 3 kids

BBG
GBG
BBG
GBG
GBG
BBB
BGG
GBG
BGB
BGG
GGG

10HailMarys · 09/12/2023 01:11

I haven't got any kids, but I'm the youngest of three and we're GBG.

My brother's got four biological kids and they're BGBG.

Theaviator · 09/12/2023 00:59

I have G B B x

KrisAkabusi · 09/12/2023 00:50

It's from the late 1970s when it was noticed that Israeli Air Force pilots were the fathers of all girls. Various theories were put forward to explain it, including the slow sperm theory. Which has continued to be repeated as a plausible explanation.

The problem is, as soon as people noticed it, it stopped happening. Pilots started having the usual near 50:50 boy girl ratio. For a hypothesis to work it has to be able to predict future trends as well. This isn't because something changed, it's because of poor statistical understanding.There was nothing special about Israeli pilots. It could have been Icelandic farmers, Angolan construction workers or Japanese waitresses. If you take any combination of nationality and occupation, through sheer chance, one of them will have a long run of same sex births. The same as if you toss a coin a million times, you are likely to see a run of twenty heads. And because prior births or tosses have no bearing on the next one, the run will naturally come to an end.

It was pure chance, nothing to do with anything occupational or biological.

poetryandwine · 09/12/2023 00:23

KrisAkabusi · 08/12/2023 20:48

This isn't true. It's a myth because of really really bad statistical analysis.

Show quote history

Can you explain why or give a reference please?

4kidsx · 08/12/2023 23:47

GGGG

Most my family has BGB though.

Flanjango · 08/12/2023 22:09

Difficult to say for sure as middle "child" was twins. But in birth order. B,g,b,g.

lifeisahamsterwheel · 08/12/2023 21:35

I have GGB most people I know with 3 have 3 of the same sex. I think it's also worth pointing out when I see these posts that it's only relative information if posters are using the same parents for the 3 kids not different dads as it's the male that determines the sex so different dads won't make the results accurate as it's not 3 from the sane gene pool.

BarbaraofSeville · 08/12/2023 21:22

@Kendodd

This link indicates that there may be a small higher chance of a third child being the same sex as a previous one, but it's quite small 52/48.

https://socratic.org/questions/a-family-has-3-children-find-the-probabilities-a-all-boys-b-all-boys-or-all-girl#621064

But you couldn't definitively know that without analysing thousands of families, and also taking account of multiple births, miscarriages and terminations.

(not a mathematician but a scientist with a passing interest in statistics).

A family has 3 children. Find the probabilities. A) all boys B) All boys or all girls C) Exactly two boys or two girls D) At least one child of each gender What are the probabilities? | Socratic

See below We have 3 children, with each one possibly being a boy or a girl. And so for each child, the probability of being a boy is 1/2 as is the probability of being a girl 1/2 A Therefore, for there to be all boys, the probability is: P("all boys")=...

https://socratic.org/questions/a-family-has-3-children-find-the-probabilities-a-all-boys-b-all-boys-or-all-girl#621064

ChangeNameLikeIChangeSocks · 08/12/2023 21:18

I have
B
G (didn't make it)
B
So not sure if my G counts as 2 or 1.5

peanutbear · 08/12/2023 21:17

BBG

Hawkerslife · 08/12/2023 21:16

BBB. I know a fair few other people that have BBB too but only one with GGG.

VickyEadieofThigh · 08/12/2023 21:11

I have no children but am the G of BGB set. My female partner is the final G of GBBG.

DollyParsons · 08/12/2023 21:07

Interesting.

Family and friends:

BBB
BBB
GGGG
BBB
GBB
BBB
BBB
GBB
GBG

PotteringAlonggotkickedoutandhadtoreregister · 08/12/2023 21:06

I have BBB

my friends have:

GBB
GGG
GBB

so all live up to your theory!

BarbaraofSeville · 08/12/2023 21:03