On Tue, 11 Apr 2006, Renaud Lancelot wrote:
> 2006/4/10, Tarca, Adi <[EMAIL PROTECTED]>:
>> 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
[EMAIL PROTECTED] University of Washington, Seattle
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