Yeah, I got a bit confused because I imagined that you’d go to the maternity ward and watch the happy mothers leaving with their babies. If the last one you saw come out was a girl, you know they’re not done. Symmetry broken. You are taking an unbiased list of possibilities and throwing out the half of them that end with a girl...
Except that to fix the problem, you end up adding an expected equal number of girls as boys.
I had it straight the first time, really. But his answer was so confusingly off that it re-befuddled me.
He did answer the question he posed, which was “What is the expected fraction of girls in a population [of N families]?” It’s not an unmeasurably-small hair. It depends on N. When N=4, the expected fraction is about .46. If you don’t believe it, do the simulation. I did.
I believe the mathematics. He is correct that E(G/(G+B)) < 0.5. But a “country” of four families? A country, not otherwise specified, has millions of families, and if that is interpreted mathematically as asking for the limit of infinite N, then E(G/(G+B)) tends to the limit of 0.5.
To make the point that this puzzle is intended to make, about expectation not commuting with ratios, it should be posed of a single family, where E(G)/E(G+B) = 0.5, E(G/(G+B)) = 1-log(2).
But as I said earlier, how is this puzzle relevant to the rest of your post? The mathematics and the simulation agree.
Estimating the mean and variance of the Cauchy distribution by simulation makes an entertaining exercise.
Thinking about betting $15,000 on a math problem, to be adjudicated by the outcome of a computer simulation, made me wonder how we know when a computer simulation would give the right answer. Showing the results for the similar-looking but divergent series is the simplest example I could think of of when a computer simulation gives a very misleading estimate of expected value, which is the problem this post is about.
(In response to a longer version of the previous post which was in response to the pre-edited version of its parent, which was opposite in nearly every way—and because it was up really briefly, I forgot that he could have seen the pre-edit version. If RK weren’t a ninja this wouldn’t have come up)
Dude, I already conceded. You were right, I said I was wrong. When I was saying I had it straight the first time, I meant before I read the solution. That confused me, then I wrote in response, in error. Then you straightened me out again.
He did answer the question he posed, which was “What is the expected fraction of girls in a population [of N families]?” It’s not an unmeasurably-small hair. It depends on N. When N=4, the expected fraction is about .46.
Yeah, I got a bit confused because I imagined that you’d go to the maternity ward and watch the happy mothers leaving with their babies. If the last one you saw come out was a girl, you know they’re not done. Symmetry broken. You are taking an unbiased list of possibilities and throwing out the half of them that end with a girl...
Except that to fix the problem, you end up adding an expected equal number of girls as boys.
I had it straight the first time, really. But his answer was so confusingly off that it re-befuddled me.
E(G-B) = 0, E(G/(G+B)) < 0.5.
He did answer the question he posed, which was “What is the expected fraction of girls in a population [of N families]?” It’s not an unmeasurably-small hair. It depends on N. When N=4, the expected fraction is about .46. If you don’t believe it, do the simulation. I did.
I believe the mathematics. He is correct that E(G/(G+B)) < 0.5. But a “country” of four families? A country, not otherwise specified, has millions of families, and if that is interpreted mathematically as asking for the limit of infinite N, then E(G/(G+B)) tends to the limit of 0.5.
To make the point that this puzzle is intended to make, about expectation not commuting with ratios, it should be posed of a single family, where E(G)/E(G+B) = 0.5, E(G/(G+B)) = 1-log(2).
But as I said earlier, how is this puzzle relevant to the rest of your post? The mathematics and the simulation agree.
Estimating the mean and variance of the Cauchy distribution by simulation makes an entertaining exercise.
Thinking about betting $15,000 on a math problem, to be adjudicated by the outcome of a computer simulation, made me wonder how we know when a computer simulation would give the right answer. Showing the results for the similar-looking but divergent series is the simplest example I could think of of when a computer simulation gives a very misleading estimate of expected value, which is the problem this post is about.
The question asked about a country. Unless you’re counting hypothetical micro-seasteads as countries, the ratio is within noise of 50%.
(In response to a longer version of the previous post which was in response to the pre-edited version of its parent, which was opposite in nearly every way—and because it was up really briefly, I forgot that he could have seen the pre-edit version. If RK weren’t a ninja this wouldn’t have come up)
Dude, I already conceded. You were right, I said I was wrong. When I was saying I had it straight the first time, I meant before I read the solution. That confused me, then I wrote in response, in error. Then you straightened me out again.
Sorry, I posted before you corrected that post. I shall edit out my asperity.
Sorry for resisting correction for that short time.
He did answer the question he posed, which was “What is the expected fraction of girls in a population [of N families]?” It’s not an unmeasurably-small hair. It depends on N. When N=4, the expected fraction is about .46.