From: harry wills <harry.wills_at_gmail.com>

Date: Thu 29 Jun 2006 - 04:46:07 EST

Date: Thu 29 Jun 2006 - 04:46:07 EST

Hi Rick,

Thanks a lot for pointing out the mistake. I changed it and now the results
match perfectly !

Harry

On 6/28/06, Rick Bilonick <rab45+@pitt.edu> wrote:

*>
*

> On Wed, 2006-06-28 at 11:04 -0400, harry wills wrote:

*> > 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
**>
**> >From my understanding of SAS, a*b means the interaction of a and b. But
**> in R, a*b is shorthand for a + b + a:b where a:b is the interaction
**> term. The way you've written the lme formula, you have time showing up 4
**> times plus you have additional main effects x1, x2, and x3. Is this what
**> you want? Maybe I'm wrong but I don't think the SAS code and the R code
**> represent the same model.
**>
**> Rick B.
**>
**>
*

-- Wills, Harry [[alternative HTML version deleted]] ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.htmlReceived on Thu Jun 29 04:57:54 2006

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