[R] Cox regression and p-values

[Cody Hamilton]

Daniel,

With regards to the use of Fisher's exact test when cell counts are less than 5, take a look at:

D'Agostino, RB, Chase, W and Belanger, A (1988). 'The appropriateness of some common procedures for testing the equality of two independent binomial populations.' 42:198-202.

Regards,
   -Cody

Cody Hamilton
Edwards Lifesciences

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Daniel Brewer
Sent: Tuesday, September 18, 2007 9:42 AM
To: r-help at stat.math.ethz.ch
Subject: [R] Cox regression and p-values

Hello,
I might be barking up the wrong tree here, but I want to make sure I
have a full understanding of this.  What I would like to know is what
tests are performed to give the p-values for each variable in the table
that is the result of coxph regression when the variables are
categorical only.

More specifically, when expected counts are less than 5 is the Fisher's
exact test used instead of the Chi^2 test?

Many thanks
Dan
--
**************************************************************
Daniel Brewer, Ph.D.
Institute of Cancer Research
Email: daniel.brewer at icr.ac.uk
**************************************************************

The Institute of Cancer Research: Royal Cancer Hospital, a charitable Company Limited by Guarantee, Registered in England under Company No. 534147 with its Registered Office at 123 Old Brompton Road, London SW7 3RP.

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