[R-sig-ME] lme: predictions variance collapses when one more level is added

[Dieter Menne]

Ben Bolker commented:

>   Sorry for snipping context here (I'm posting via gmane, which doesn't
> like that).  If I use  weights=varIdent(form=~1|treat)) rather than
> weights=varPower() (i.e. residual variance varies by treatment group,
> rather than as a power function of the estimated mean), I get what
> seem (at least at a quick glance) to be reasonable results.

You are right; I received a similar comment from Ariel Muldoon off-list. I
admit that I have tried it, but most have done some stupid syntax mistake so
it go away unnoticed.

While it is a solution, I still do not understand what really happens with
the prediction. And, assuming I am using lmer, what should I do? I noted the
same collapsing effect.


Dieter