[R] lme (or lmer) question

[Bert Gunter]

Folks:

In the following mixed effect model, the "x" and residual variance
components are nonidentifiable. Yet lme() (or the equivalent in lmer())
happily produces an answer in which the sum of the variance components is
the correct estimate of the single variance parameter. Why? -- i.e. why
doesn't lme complain?

x <- 1:50
y <- rnorm(50)
m1 <- lme( y ~ 1, rand = ~1|x)


Many thanks,

Bert Gunter
Genentech Nonclinical Statistics