[R] Fit unequal variance model in R

Dieter Menne dieter.menne at menne-biomed.de
Wed Apr 1 18:34:12 CEST 2009



Feng, Jingyu wrote:
> 
> I'am trying to develop some code if R, which would correspond to what I
> did in SAS.
> The data look like:
> 
> Treatment    Replicate    group1      GSI
> 
> ..
> The SAS code is:
> proc mixed data=data_name order=data method=ml; *scoring=10;
>       classes group1;
>       model GSI=group1/residual influence solution;
>       repeated /group=group1;
> 
> run;
> 
> Basically, I need different variance for each treatment group. I want to
> do the similar thing in R.
> 
> Here is what I get so far:
> lm1<-lme(response~treatment,data=o,random=~1|as.factor(dummy),weights=varIdent(form=~1|treatment),method="ML")
> 
> There should no random term in the model. However If I don't specify one,
> lme won't work, so I made a dummy variable, which equals to 1 for every
> observation.
> 
> 

The much underused (quote Frank Harrell) gls in package nlme should do that.
Quote PB (p250): It can be viewed as an lme function without the random
argument.

Dieter
-- 
View this message in context: http://www.nabble.com/Fit-unequal-variance-model-in-R-tp22829549p22830566.html
Sent from the R help mailing list archive at Nabble.com.




More information about the R-help mailing list