[R] Cochran-Mantel-Haenszel problem

[Peter Dalgaard]

Frank E Harrell Jr <feh3k at spamcop.net> writes:

> On Thu, 11 Dec 2003 14:42:07 +0100
> <Arne.Muller at aventis.com> wrote:
> 
> > Hello,
> > 
> > I've tried to analyze some data with a CMH test. My 3 dimensional
> > contingency tables are 2x2xN where N is usually between 10 and 100.
> > 
> > The problem is that there may be 2 strata with opposite counts (the 2x2
> > contigency table for these are reversed), producing opposite odds ratios
> > that cancle out in the overall statistics. These opposite counts are
> > very important for my analysis, since they account for a dramatic
> > difference.
> > 
> > Could you recommend alternative tests that take account for opposite
> > counts? Would you suggest a different strategy to analyze such data?
> > 
> > 	thanks a lot for your suggestions,
> > 
> > 	Arne
> > 
> 
> I'm not sure about your specific problem, but in general you might think
> of this as a binary or multinomial logistic model with strata x treatment
> interactions, and get pooled treatment main effect + interaction effects,
> which are equivalent to testing whether treatment is associated with
> response for ANY stratum (without cancellation when signs of effects are
> reversed).  With the Design package, for example, you can do this easily
> when the response is binary or ordinal:
> 
> library(Design)
> f <- lrm(y ~ treat*strat)
> anova(f)   # prints multiple d.f. test for treat as either main effect or
> effect modifier
> 
> Of course when you allow for a more general model such as this, the power
> is diluted into multiple degrees of freedom when the effects really do not
> vary very much over strata.

Also note the woolf() function given in the examples section of the
help for mantelhaen.test.

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907