Ross Darnell <[EMAIL PROTECTED]> writes: > I would like some advice on how if possible, to test the following > > I have subjects each measured several times. The subjects are sampled > from 3 subpopulations (groups). The question is "Is the > between-subject variance the same for the three groups?" > > The "null" model is > > lme0 <- lme(y~group,random=~1|subject) > > I did think that the model that defined a specific between-subject > variance for each group was > > update(lme0,.~., weights=varIdent(form=~1|group)) > > but I am not sure.
I think you have it right. You should then compare the two fitted models using the anova generic, which will provide a likelihood ratio test statistic and a p-value based on a chi-squared reference distribution. Regard the p-value as an approximation. ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help