Dear freesurfer experts, I'm using Qdec and I want to control for age (a continuous variable) and sex (f,m or 1,0).
Do I need to center age (i.e., subtract the score from its mean) before I select it as a nuisance factor? Do I need to center sex? I found that selecting age_centered as a nuisance factor vs. selecting age_uncentered as a nuisance factor led to very different results… not sure what is the correct way to go. In brief, if I want to control for age and sex, which of the following is the correct way to go? 1. Center neither age nor sex (f,m). Then choose age_uncentered as a nuisance factor, but sex_uncentered as a discrete/fixed factor. 2. Center age but not sex (f,m). Then choose age_centered as a nuisance factor, but sex_uncentered as a discrete/fixed factor. 3. Center age but not sex (1,0). Then choose both age_centered and sex_uncentered as nuisance factors. 4. Center age and sex (1,0). Then choose both age_centered and sex_centered as nuisance factors. Thanks in advance! Daniel -- Yung-Jui "Daniel" Yang, PhD Postdoctoral Researcher Yale Child Study Center New Haven, CT (203) 737-5454
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