ancova analysis of pre/post data

[duo wan <duo_wan@yahoo.com>]

Hello:

 

I have a data set with pre and post measurements for 4 different treatment groups. My interests will be 1: investigate the differences of post measurements among 4 different groups 2: investigate if there is a change from pre-period to post-period.

 

I think I can answer the first question with ancova with pre measurement as covariate

lm(post~treatment+pre+treatment*pre,data="">

 

but I doubt Ancova approach can answer the 2nd question of pre/post change. is it reasonable to use two way anova to handle this two periods repeated measurement data? if not, how can we model covariance structure for two periods?

 

any suggestion will be appreciated.

 

duo wan

 

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