Hi all, I posted a long question for this the other day, but no one has responded. Here is a short version those of you who are very busy might have time to read. Any advice would be greatly appreciated. I have a growth model where 2 groups differ on the outcome at baseline. How do I get the growth model adjusting for this difference (or making the groups equivalent at baseline, such as in ANCOVA)? Predict growth from a 2nd(person)-level covariate of baseline scores (i.e., a growth:baseline covariate interaction in a mixed model)? Does it make sense to add the baseline covariate as a predictor of the intercepts as well as the slopes or is this completely redundant with a model where time is coded so that 0 = baseline? Thanks again. - DC
Adjusting for baseline differences in growth models
2 messages · D Chaws, Ken Beath
1 day later
On 03/09/2008, at 1:34 PM, D Chaws wrote:
Hi all, I posted a long question for this the other day, but no one has responded. Here is a short version those of you who are very busy might have time to read. Any advice would be greatly appreciated. I have a growth model where 2 groups differ on the outcome at baseline. How do I get the growth model adjusting for this difference (or making the groups equivalent at baseline, such as in ANCOVA)? Predict growth from a 2nd(person)-level covariate of baseline scores (i.e., a growth:baseline covariate interaction in a mixed model)? Does it make sense to add the baseline covariate as a predictor of the intercepts as well as the slopes or is this completely redundant with a model where time is coded so that 0 = baseline?
Fitting a mixed-effects model for the post baseline outcomes only with the baseline as a covariate affecting only the intercept seems sensible. This is the same as the ANCOVA but with repeated measures. Ken
Thanks again. - DC
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