"Herman Rubin" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> In article <[EMAIL PROTECTED]>,
> Duncan Smith <[EMAIL PROTECTED]> wrote:
>
> >"wuzzy" <[EMAIL PROTECTED]> wrote in message
> >news:[EMAIL PROTECTED]
> >> I asked this elswhere, this group may be more appropriate, appologies
> >> for simple question?
>
> >> Can someone describe an algorithm in MS Excel to find the posterior
> >> distribution given a likelihood function (=BINOMDIST) and a prior
> >> distribution (=NORMDIST mu=0, sigma=0.05)?
> >> I know that it is proportional to L*P (likelihood times prior).
> >> [anyone know how to calculate the denominator in excel?]
>
> >> But what is an exact algorithm?!
>
> >> For instance I was considering sampling 10 random parameters in ten
> >> columns
> >> of BINOMDIST()*NORMDIST(from 1..10) for each case. But what does this
> >> product tell me? how do I actually plot the distribution?
>
> >> Thanks
>
> >Does it make sense to have a Normal prior (particularly with mu=0) with a
> >Binomial likelihood? If a Beta prior makes at least as much sense it
makes
> >the maths much easier.
>
> >Duncan
>
> I see two common errors here. In principle, the prior, or
> the operational loss-prior combination, should come from
> the user, with no consideration of computational ease. It
> MAY be that a conjugate prior provides a reasonable
> approximation, or it may not. My prior distribution for
> baseball players' batting averages is definitely not well
> approximated by a Beta distribution.
>
> The other error is that, while the logistic is a model for
> probabilities, the parameters of the logistic are not the
> direct calculation of the probabilities. In fact, I have
> seen the logistic model as a conditional normal model.
> Computationally, one can give priors easier to work with,
> but they will be logistic type priors. Numerical integration
> is an art, especially if it is in more than one dimension.
> --
> This address is for information only. I do not claim that these views
> are those of the Statistics Department or of Purdue University.
> Herman Rubin, Department of Statistics, Purdue University
> [EMAIL PROTECTED] Phone: (765)494-6054 FAX: (765)494-0558
Herman,
I was simply querying the OP's prior to get a better handle on
the problem. I wouldn't encourage the OP to use a conjugate prior unless it
makes "at least as much sense" as any other prior. :-)
Duncan
.
.
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