[R] testing differences between slope differences with lme
dede01 at codon.nih.gov
Tue Apr 10 01:18:54 CEST 2007
i have a mixed effect model which gives slope and intercept terms for 6
groups (diagnosis (3 levels) by risk group(2 levels)). the fixed part of
the model is --
brain volume ~ Diagnosis + Risk Group + (Risk Group * age : Diagnosis) - 1
thus allowing risk group age/slope terms to vary within diagnosis and
omitting a nonsignificant diagnosis by risk group intercept (age was
i am interested in whether differences in risk groups' developmental
trajectories are different for different diagnoses.
the last three (of 10) fixed effect estimates are estimates for the
age/slope differences between risk groups for the 3 diagnostic groups.
my question is this -- how do i test if the 3 differences are statistically
different from each other?
i can do this in SAS but the answer in R is eluding me.
thanks in advance,
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