[R] Adjusting for initial status (intercept) in lme growth models

[Dieter Menne]

D Chaws <cat.dev.urandom <at> gmail.com> writes:

> Say, for instance you want to model growth in pituitary distance  as a
> function of age in the Orthodont dataset.
> 
> fm1 = lme(distance ~ I(age-8), random = ~ 1 + I(age-8) | Subject, data =
> Orthodont)
> 
> You notice that there is substantial variability in the intercepts (initial
> distance) for people at 8 years, and that
> this variability in initial distance is related to growth over time:

Looks like a perfect example to use parameter weight=varPower(something)  in
lme; you could use some power function of the initial distance. See Chapter 5.2
in Pinheiro-Bates.

Dieter