Message-ID: <4B44529E.2080500@cam.ac.uk>
Date: 2010-01-06T09:06:38Z
From: robin hankin
Subject: Generating data from Null Distribution
In-Reply-To: <b137ab71001060016k55e83a23xbe017fa1faafef12@mail.gmail.com>
Jim
the 2x2 case is reasonably straightforward because the support
is quite a small set.
With the aylmer package you could do this:
> a <- matrix(c(1,5,7,8),2,2)
> sample(seq_along(allprobs(a)),100,replace=TRUE,prob=allprobs(a))
[1] 3 2 4 1 3 4 4 4 4 3 3 4 4 2 3 4 5 4 3 3 4 4 2 1 4 3 3 3 4 2 3 4 3
4 4 2 3
[38] 3 4 3 4 4 3 4 3 2 3 4 2 3 3 4 2 3 2 3 1 3 5 1 3 2 3 3 4 5 2 5 1 3
3 4 3 5
[75] 4 2 3 4 5 2 3 4 4 3 3 3 4 3 4 6 3 3 4 2 4 4 2 3 2 3
>
For bigger tables the matter becomes quite complicated but you
can use randomboards() of the aylmer package, which generates
random samples using the Metropolis-Hastings algorithm.
HTH
Robin
Jim Silverton wrote:
> Hello everyone,
>
> Can someone tell me exactly how to generate data from a null distribution
> for the fisher exact test? I know I have to use the hypergrometric but
> exactly what commands do I use?
>
> Jim
>
> [[alternative HTML version deleted]]
>
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--
Robin K. S. Hankin
Uncertainty Analyst
University of Cambridge
19 Silver Street
Cambridge CB3 9EP
01223-764877