odds of having 11 children of the same sex

I just watched a TV show that had a woman who allegedly had 11 children, all boys. Am I right in thinking that the odds of this happening are 1 in 2 to the 11th power or 1/2048? Certainly statisticly possible, but also definitively unlikely.

Any replies are appreciated,

Your calculation is correct, assuming the odds of one gender over the other is in fact one in two. Studies have suggested this may not be the case, but it’s close enough.

How large is the bias and towards what sex? I imagine it must be small.

About 105 boys are born for every 100 girls. Makes the odds against 11 boys in a row somewhat less unlikely.

Your odds are only for all families with eleven children. This has to be multiplied by the odds of a family having 11 children of any sex.

There also appears to be a small bias toward one gender or another dependent on the gender of previous children - particularly if you have had boys, but only very slightly:

Study reported here


Also assuming that there isn’t a biological reason that Y bearning sperm are not being favored for that specific couple.

This is the important point. There are plenty of couples who are biologically incapable of producing children of one sex or the other. Doesn’t matter how many kids they have, they will always be all the same sex.

What do you mean by “definitively unlikely”? I don’t know how many women there are in the world who have 11 children, but it wouldn’t surprise me if the number were well over 2048. In that case, even if the probability of any one set of 11 children being all boys were 1/2048, it would be extremely likely that some woman, somewhere, had 11 boys.

I knew, even before opening this thread, that it had already degenerated into pointless nitpickery. By any reasonable standard, the answer is 1 in 2^11. Let it go, people. Let it go.

My aunt quit after 6 boys.

I think we’re gonna need a cite for that.

Actually, it’s 1 in 2^10. The odds that your first kid has some sex (1) multiplied by the odds that the next ten have the same sex as the first one (1/1024).

Well, the OP asked for the odds of “this” happening. It’s unclear whether “this” refers to all the kids being boys or all being the same gender. So it’s either 1 in 2^10 or 1 in 2^11, depending on which one he meant.

Dammit, now I’m pointlessly nitpicking!

If you read the thread title, there’s a hint that, I feel, clears up this ambiguity. :slight_smile:

If daddy, biologically, can’t throw that X chromosome, it will be “boy” everytime.

What the heck does this mean? The odds that a family with 11 children has 11 children of any sex is 100%.

It may be worth noting that the chance of getting on a TV show devoted to the interesting distribution of the sex of your 11 children improves if they are all boys.

Needscoffee wrote:
Your odds are only for all families with eleven children. This has to be multiplied by the odds of a family having 11 children of any sex.

I think Needscoffee meant something like “What are the odds that any two people who start having kids will end up with exactly 11 kids of the same gender”. (I presume that this is a misunderstanding of the original question, which presumably is “Given that a couple has 11 kids, what are the odds that all 11 will be the same gender”.)

My mother was the youngest of nine girls.