Thanks for the help Dimitris,

However I still have a question, this time I'll be more specific,

the following is my SAS code



proc mixed data=Reg;
        class ID;
        model y=Time Time*x1 Time*x2 Time*x3 /S;
        random intercept Time /S type=UN subject=ID G GCORR V;
        repeated /subject = ID R RCORR;
run;    **

(Type =UN for random effects)



The eqivalent lme statement I am using is :

reglme  <- lme(y ~ Time+Time*x1+Time*x2+Time*x3, data=Reg, random = ~ Time |
ID)



When I compare the results, the values differ by considerable margin; I
suppose this is due to the Random effects covariance structure. R output
tells me that the structure is



"Structure: General positive-definite, Log-Cholesky parametrization"



Hence the problem for me is how to control this structure in R. Any help
would appreciated

Thanks

Harry


On 6/28/06, Dimitris Rizopoulos <dimitris.rizopoulos@med.kuleuven.be> wrote:
>
> AFAIK lme(), by default, estimates the covariance between two or more
> random-effects, thus you do not have to specify anything. You're
> probably looking for something like:
>
> fit <- lme(y ~ time * treat, random = ~ time | subject)
> fit
> summary(fit)
>
>
> I hope it helps.
>
> Best,
> Dimitris
>
> ----
> Dimitris Rizopoulos
> Ph.D. Student
> Biostatistical Centre
> School of Public Health
> Catholic University of Leuven
>
> Address: Kapucijnenvoer 35, Leuven, Belgium
> Tel: +32/(0)16/336899
> Fax: +32/(0)16/337015
> Web: http://med.kuleuven.be/biostat/
>     http://www.student.kuleuven.be/~m0390867/dimitris.htm
>
>
> ----- Original Message -----
> From: "harry wills" <harry.wills@gmail.com>
> To: <r-help@stat.math.ethz.ch>
> Sent: Wednesday, June 28, 2006 9:02 AM
> Subject: [R] Linear Mixed Effects
>
>
> > Hi,
> > I have implemented the lme in SAS and specified the random effects
> > covariance structure as unstructured using the statement "random /
> > type=UN"
> > I want to specify same in R but not able to know how to do it.
> > Can anyone please advise me on how to proceed.
> > Thanks
> >
> >
> > --
> > Wills, Harry
> >
> > [[alternative HTML version deleted]]
> >
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>
>


-- 
Wills, Harry

	[[alternative HTML version deleted]]

