The condition is that one of the offspring (not necessarily the ith
offspring) is known to be affected. The status of other m-1 offsprings is
unknown.
Thanks,
James.
Richard A. Beldin <[EMAIL PROTECTED]> wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> The ambiguity is in the initial statement. "Given an offspring is
affected" can
> mean
> 1) We know that the i'th offspring is affected and the statuses of the
other
> m-1 are unknown
> 2) We know the status of all m offspring and exactly one is affected.
> 3) We know the status of all m offspring and x (>0) are affected.
>
> Use the most specific condition that you can confirm.
>
> James Cui wrote:
>
> > I have a problem of calculating a conditional probability, and want to
know
> > what is the right formula.
> >
> > Suppose a family consists of two parents and m offsprings. Consider a
> > disease that affects both genders equally. Given an offspring is
affected,
> > what is the probability that neither two parents nor other m-1
offsprings
> > are affected. Am I right to use the following formula ?
> >
> > Pr(F1=0; F2=1) / Pr(F2>0)
> >
> > where F1 is the number of affections in parents, and F2 is the number of
> > affections among offsprings.
> >
> > Thanks,
> > James.
>
