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Hi Michiko,

Please see below:


On 29 May 2017 at 12:18, Michiko <[log in to unmask]> wrote:
Hi Anderson,

Thanks for your reply and for sharing your insights.

So to be absolutely certain:

1. I understand in your earlier reply that you said mean centering is not necessary if I am not testing the variables on their own. However, if I were to be running only one model that includes patient-specific regressors and would like to test the effect of patient-specific regressors (e.g. duration of illness) on FA, would mean centering be necessary? How should I mean center this - e.g. across HC, pt grp 1 and pt grp 2? Or only across/within pt groups?

Mean-centering is only about data that is in the model, not data that doesn't go into it, so if you run a model with group 1, mean centering would be within group 1 only. However, you could forget about mean-centering and simply include an intercept in the model.

 

2. If I employ the 2-model design, would I have to recreate the mean template with only the pt groups? Might there be any issues with this?

I don't think it's a problem to use the same template given that all comparisons will be within-group in this second model.

All the best,

Anderson

 

Thanks again very much and I appreciate your suggestions on the above.