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

Angela Brant angela.brant at googlemail.com
Thu Jul 26 18:28:10 CEST 2012

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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