On Tue, 11 Apr 2006, Thomas Lumley wrote: > 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
Not so: some have 3 and some have 2, and the two levels of T are not quite balanced (29/28). > and no covariates that vary within a person. The independence and > exchangeable working correlations will give identical answers. They do not in this case (nor should they, I believe). -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
