Message-Id: <l03102800b34656a54a34@[153.90.236.25]>
In-Reply-To: <371F0C7B.693A@ousd.k12.ca.us>
Date: Fri, 23 Apr 1999 11:02:06 -0600
To: "Pinhole Listserv" <pinhole@exploratorium.edu>
From: Steven Eiger <eiger@montana.edu>
Subject: Re: pinhole probability
>Hey pinholers, a probability question:
>
>Let's pretend that you meet a person and she says that she has only
>one sibling. What is the probability that her sibling is a boy? How
>about a girl? I'm pretty sure that it is not 50:50....
>
>(So, in real life, if you meet a woman with one sibling, is there
>really a better chance of her having a brother than a sister?)
>
>Stumped in Oakland
>
>--
>‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡
>
>Ian Bleakney;
I am not a statistician. But my guess is to treat this like flipping
coins. There are four possibilities two heads, two tails, a head followed
by a tail and a tail followed by a head. Since we have eliminated one by
knowing the sex of one sib, and we do not know whether she was the first or
second sibling, I would guess that there is twice the likelihood of her
sibling being of the opposite sex, relative to the same sex. I would also
guess that there is a 50% chance I am right about this. I have had this
explained to me several times and it never seems to stick. Steve Eiger.
Steven Eiger, Ph.D.
Departments of Biology and the WWAMI Medical Education Program
Montana State University - Bozeman
Bozeman, MT 59717-3460
Voice: (406) 994-5672
E-mail: eiger@montana.edu
FAX: (406) 994-3190