Hi Donald and Doug, Thanks for advice. Can I be a little bit clearer as I suspect I need a little more guidance.
When comparing controls (gp c) and whole patient group (gp p) I see interesting differences in area (DOSS model after checking for no interaction and with age and ICV as correction factors). I also see an interesting interaction between age and group (DODS model with ICV as nuisance factor) such that that thickness correlates stronger with age in one group compared to another group. The patient group can be split into 4 subgroups (gp p1 to gp p4) depending on level of an endogenous substance. I want to see whether when running gp c against gp p1, if the interaction between group and age (for thickness) is stronger/weaker than the interaction when running gp p4 against gp c. I also want to see whether differences in area between a subgroup and controls are bigger/smaller compared to differences between other subgps and controls. To do this can I use the original method (granted power will b smaller) or if I follow the method suggested by Donald should I demean individually within subgroups. Also is this kind of model qdec friendly, and if not could you offer any guidance on design matrix and contrasts. Hope i make some sense ! Thanks. Mahinda _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.
