It sounds like you need a conjunction to show that P4 > P1 AND P1 > C Does that make sense? If so, then run the analysis as Donald suggests, creating contrast matrices for the above contrasts. Then run mri_concat --conjunct p1gtc/sig.mgh p4gtp1/sig.mgh --o conjunction.mgh
doug On 11/19/2012 01:36 PM, Mahinda Yogarajah wrote: > 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 > > -- Douglas N. Greve, Ph.D. MGH-NMR Center gr...@nmr.mgh.harvard.edu Phone Number: 617-724-2358 Fax: 617-726-7422 Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting FileDrop: www.nmr.mgh.harvard.edu/facility/filedrop/index.html Outgoing: ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/ _______________________________________________ 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.
