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cassell
2004 Sep 21
1
lme RE variance computation
As I understand it lme (in R v1.9.x) estimates random effect variances
on a log scale, constraining them to be positive. Whilst this seems
sensible, it does lead to apparently biased estimates if the variance is
actually zero - which makes our simulation results look strange. Whilst
we need to think a bit deeper about it - I still haven't got my head
around what a negative variance could