[R] p values for a GEE model

[Thomas Lumley]

On Tue, 11 Apr 2006, Renaud Lancelot wrote:

> 2006/4/10, Tarca, Adi <atarca at med.wayne.edu>:
>> Hi all,
>>
>> I have a dataset in which the output Y is observed on two groups of
>> patients (treatment factor T with 2 levels).
>>
>> Every subject in each group is observed three times (not time points but
>> just technical replication).
>>
>> I am interested in estimating the treatment effect and take into account
>> the fact that I have repeated measurements for every subject.
>>
<<Snip>>
>> I would like to use also as a variant analysis a Generalized Estimation
>> Equation Model, like
>>
>>                 library(gee)
>>
>>                 summary(gee(Y~T,id=P,data=data))
>
> Beware: the default within-group correlation structure is independence
> in the gee function (see argument corstr). I think you want an
> exchangeable correlation structure, i.e. the same within-group
> correlation for all the measurements:


He has a linear model with the same number of observations for each person 
and no covariates that vary within a person. The independence and 
exchangeable working correlations will give identical answers.


 	-thomas

Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle