Cox regression and p-values
I'll throw in a more recent citation: Chi-squared and Fisher-Irwin tests of two-by-two tables with small sample recommendations Stat in Med 26:3661-3675; 2007 http://www3.interscience.wiley.com/cgi-bin/abstract/114125487/ABSTRACT to which Frank Harrell has offered some comments here (bottom of page): http://biostat.mc.vanderbilt.edu/twiki/bin/view/Main/DataAnalysisDisc HTH, Marc Schwartz
On Tue, 2007-09-18 at 11:08 -0700, Cody Hamilton wrote:
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
-----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