[R] Exact test in nxm contingency table
tlumley at u.washington.edu
Wed Sep 17 22:00:10 CEST 2008
On Wed, 17 Sep 2008, Peter Dalgaard wrote:
>fisher.test(...., simulate.p.value=TRUE) might be more direct. Also
>works for chisq.test().
>And, contrary to popular belief, fisher.test() does work for larger
>than2x2 tables, although you may run into space/time limitations.
The 'exact' test computations do suffer from roundoff error if your tables
are too large. I think we saw a 3x11 table that had problems.
It would be nice to see if the original Mehta & Patel algorithm TOMS 643
is more accurate, but I haven't been able to find code: it seems to have
been replaced everywhere by the faster Clarkson et al code.
Thomas Lumley Assoc. Professor, Biostatistics
tlumley at u.washington.edu University of Washington, Seattle
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