Call me a geek, but the BBC News website and various PhD’s they quoted are just plain wrong.
BBC News website

Sure, the isolated probablity of having a baby boy is 50%. However, you cannot take that event in isolation – there is prior history. You need to consider the law of entropy – that the world tends towards disordered events. Therefore, the probability of having a baby boy given that you already have three boys is 50% x 50% x 50% = 12.5%. So in reality the Beckhams will be very unlucky to have a boy this time.

Sorry for the boring topic. I just hate bad science.

er… er… dont agree

I just hope the poor little sod wasn’t conceived in Stoke on Trent!

nope – it will always be 50/50 same as tossing a coin

You are confusing the odds of having 4 boys in a row which is low and worked out like you do – but once you have 3 children the odds of the 4th being a boy remain 50 / 50.

Same as tossing a coin.

If you can be bothered, there’s a rather long explanation of a similar scenario here.

high horse fail

Yes and no.

The probability of having a bay boy is 50%. It is an independent event.

The probability of having three baby boys in row is 50*50*50 = 12.5%

This is not the the same probability that the third baby will be a boy.

You are stating “given that …” The system know nothing of what happened beforehand, I think it’s you use of the language “given that” as this implies a conditional probability.

How does the sex of one child affect which sperm fertilises an egg?

50 50, new outcome has no memory.

You’re wrong. The event is isolated because the other events have already happened. There’s a 50/50 chance.

You need to brush up on your understanding of probability. Risk by Dan Gardner is a good book to start with. That has loads of examples that prove the way probability calculations work – and explains why seemingly improbable things actually happen all the time.

Sorry for the boring topic. I just hate bad science.

I hate bad statistics. Biology aside, probability does not have memory. Flip a coin as many times as you like the chance of it coming up heads is 50% even if it came up heads the previous 100 times.

nope – it will always be 50/50 same as tossing a coin

You are confusing the odds of having 4 boys in a row which is low and worked out like you do – but once you have 3 children the odds of the 4th being a boy remain 50 / 50.

Same as tossing a coin.

I beg to differ. It is precisely the fact that we know that they have already produced three boys that determines the probability of the next baby being a boy. Four boys in a row is just a different way of saying having four boys out of four. More evidence here (near the end).

fanatic278 – Member
If you can be bothered, there’s a rather long explanation of a similar scenario here.

This is a different situation. The game show host know where the goat is and acts accordingly. There for a conditional situation.

Must try harder! 🙂

LOL! Yes we may know what has happened but that egg and sperm haven’t a clue what’s happened before!

Right. I’m wrong. I think….

Just delved into it deeper. Mr Elefant has turned me around. And this : http://en.wikipedia.org/wiki/Gambler’s_fallacy

This is from your link too!

Although we often hear the “statistic” that you are 30% or even 70% more likely to keep having the same gender, this is just an old wives tale. It is NOT a fact. The truth is, your odds stay pretty close to 50% for each child and only vary slightly.

What if they concieved on a conveyor belt…?

FWIW I think the two scenarios are different, with the game show host confunding the situation and adding information into the system that is not there in case of conception.

Biologically it’s very unusual to have a excess of Y sperm, hence it’s still just almost certainly chance that the Beckhams have three boys and it’s 50:50 whether they will have a boy or girl.

saying having four boys out of four.[/quote]

P(boy boy boy boy)=0.5^4
P(girl boy boy boy)=0.5^4
P(Boy girl boy boy)=0.5^4
P(Boy boy girl boy)=0.5^4
P(Boy boy boy girl)=0.5^4

P(of NOT having 4 boys in a row)=1-P(boy boy boy boy)
=P(girl boy boy boy)+P(Boy girl boy boy)+P(Boy boy girl boy)+P(Boy boy boy girl)
=1-0.5^4

All four iterations have equal probability, but P(B B B B) seems to have order and devices us slightly. Probability is simple in some ways but really easy to get wrong because the result frequently seem wrong.

It’s probably that only his right (boy) bollock is working. His left’un probably got squashed somewhere along the line so the new nipper will be another gruesomely-named spoilt male clothes-horse.

National lottery are guilty of the same inaccurate description of probability going on about how many times such a number has been selected. Totally irrelevant. They all have an equal chance…assuming the balls and machines have no inbuilt variations which lead to increased selection

pedlad – Member
National lottery are guilty of the same inaccurate description of probability going on about how many times such a number has been selected. Totally irrelevant. They all have an equal chance…assuming the balls and machines have no inbuilt variations which lead to increased selection

They don’t need to really they can rely on truthful advertising.

888 Had a n advert on the tube a few years ago 97% payback.
Nice you are advertising that for every pound I put into your casino I get 97 p back.

The Mash have an interesting take on it…

Pointy wife – LOL

once she’s had the kid she needs to get somebody to ask her the sex and birth-day of at least one of her kids

suddenly she’ll have 4 girls – by magic

(no, I still don’t believe the 33% “story”)

Edit: Withdrawn.

i’m a berk.

let it be known henceforth.

Poppa

Luckily you managed to withdraw that within your allotted 13 minutes. Unfotunately for David he didn’t.

Well, you non-Bayesiansc are missing a point. Given that they have conceived 3 boys already, it is more likely they will conceive another boy.

Try this scenario, we toss a coin, which comes down heads 100 times in a row. what do you want to bet on? Heads or tails?

Heads!!!!
I claim my £20 as I pretty sure its a double headed coin.

Sorry. I have to ask this but WTF ?

How does the sex of one child affect which sperm fertilises an egg?

I wouldn’t be surprised if they have had medical intervention to ensure a female embryo, it’s legal in the states

Heads!!!!
I claim my £20 as I pretty sure its a double headed coin.

How sure?

Enough to stake £20 on it !

ok… Ready?

1,2,3,4,…………….99,100 GO !

i thought that women were more likely to have male offspring the older that they got?? or is that a misnomer?

I just hope the poor little sod wasn’t conceived in Stoke on Trent!

Worry ye not. 50% he/ 50% she/ 50% it was conceived in Ecclefechan

ah, it was heads!

do you take paypal?

Double or quits ?