Yes, use the DODS model to look for an interaction. In your case, you will have four regressors: Group1 Intercept, G2 Intercept, G1 slope, G2 slope, so test the interaction with the contrast [0 0 1 -1]. If there is no interaction, then run with a DOSS model and contrast [1 -1 0] to look for a difference between groups. doug
On 05/16/2012 09:09 PM, ZhiLiangLong wrote:
Hi all: I'm a little confused about the DODS model and DOSS model. I have two groups (patient and control) and one covariate (age), and I want to compare the diffirence of thickness between the groups with age as the covariate. In DODS model, is the process the analysis of variance substantially (group is a factor and age is another factor)? Generally, if there is no interaction between age and group, then i can re-run with the DOSS model to increase the statistical power.But i don't know how to determine whether there is no interaction . I hope someone give me some suggestions.
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