[R] Testing significance of interaction between group and longitudinal change for part of the age range in a mixed linear model

Bert Gunter gunter.berton at gene.com
Thu Jul 26 18:55:11 CEST 2012

1. Your post is unacceptable (imho, of course). Read the bottom of
this message (re: "posting guide") and re-post properly.

2. This is not an R-help question. Re-post on r-sig-mixed-models -- or
perhaps on a non-R statistical forum like stats.stackexchange.com, as
this appears to have little to do with R, per se.

-- Bert

On Thu, Jul 26, 2012 at 9:28 AM, Angela Brant
<angela.brant at googlemail.com> wrote:
> Hi all,
> I've fit a mixed linear model to some longitudinal data. I'm interested in the differences in patterns of decrease in the dependent variable according to group status, and my hypothesis particularly predicts a difference between the groups in trajectory of change at between specific ages. The data shows a significant interaction between group and the linear and quadratic effects of age, but I don't know if there is a way to assess this interaction for one part of the age range, or if I need to be able to do so in order to interpret my results as bing supportive of my hypothesis.
> Thanks for any help/advice!
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.


Bert Gunter
Genentech Nonclinical Biostatistics

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