Re: [R] fisher table probability

From: array chip <arrayprofile_at_yahoo.com>
Date: Fri 03 Feb 2006 - 09:54:32 EST


Thanks for pointing. This is my simple function for doing this, just like to share if anyone ever needs it:

   ## x is a rxc table
tabprob<-function (x) {
  tmp<-0
  for (i in 1:dim(x)[1]) {
    tmp<-tmp+lgamma(sum(x[i,])+1)
    for (j in 1:dim(x)[2]) {

      if (i==1) tmp<-tmp+lgamma(sum(x[,j])+1)
      tmp<-tmp-lgamma(x[i,j]+1)

    }
  }
  tmp<-tmp-lgamma(sum(x)+1)
  exp(tmp)
}

> On Thu, 2 Feb 2006, array chip wrote:
>
> > Thanks for the suggestion! what if the dimensions
> of
> > the table is greater than 2, say 3x4?
>
> Look at the references quoted on the help page for
> the formula: the
> simulation code for p-values in R-devel makes use of
> it and it is easy to
> compute via lgamma.
>
> >
> > --- Prof Brian Ripley <ripley@stats.ox.ac.uk>
> wrote:
> >
> >> On Wed, 1 Feb 2006, array chip wrote:
> >>
> >>> Hi, is there a way to generate the table's
> >> probability
> >>> when doing the fisher's exact test on a 2x2
> table?
> >> The
> >>> fisher's exact test gives the p value, but not
> the
> >>> probability for the table.
> >>
> >> Call dhyper, as fisher.test itself does.
> >>
> >> --
> >> Brian D. Ripley,
> >> ripley@stats.ox.ac.uk
> >> Professor of Applied Statistics,
> >> http://www.stats.ox.ac.uk/~ripley/
> >> University of Oxford, Tel: +44 1865
> >> 272861 (self)
> >> 1 South Parks Road, +44 1865
> >> 272866 (PA)
> >> Oxford OX1 3TG, UK Fax: +44 1865
> >> 272595
> >>
> >
> >
> > __________________________________________________
> > Do You Yahoo!?

> protection around
> > http://mail.yahoo.com
> >
> >
>
> --
> Brian D. Ripley,
> ripley@stats.ox.ac.uk
> Professor of Applied Statistics,
> http://www.stats.ox.ac.uk/~ripley/
> University of Oxford, Tel: +44 1865
> 272861 (self)
> 1 South Parks Road, +44 1865
> 272866 (PA)
> Oxford OX1 3TG, UK Fax: +44 1865
> 272595
>



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