Rense,
how about
weights = varPower(form = ~ schavg)
or
weights = varConstPower(form = ~ schavg)
or even
weights = varPower(form = ~ schavg | type)
Yuo might find Pinheiro and Bates (2000) to be a valuable investment.
I hope that this helps,
Andrew
On Sun, Jun 10, 2007 at 04:35:58PM +
Dear All,
I'm trying to model heteroscedasticity using a multilevel model. To
do so, I make use of the nlme package and the weigths-parameter.
Let's say that I hypothesize that the exam score of students
(normexam) is influenced by their score on a standardized LR test
(standLRT). Students
