Hi Daniel, yes, it is true for an unbalanced design. The values that are being compared are averages. If you compared the average of a group of 15 to the average of a group of 5, you would not scale the averages by the number of members in the group.
doug daniel geisler wrote: > > Hi Freesurfers, > > > > I am currently dealing with some examples of group analysis from > freesurfer-wikipages (see > http://surfer.nmr.mgh.harvard.edu/fswiki/Fsgdf4G0V). Could you please > give some clarifications in the following scenario: > > > > Assume we have four groups MaleRight, MaleLeft, FemaleRight, and > FemaleLeft (from factors gender and handedness). Now we want to set a > contrast that is equivalent to the question: "Is there a difference > between Males and Females regressing out the effects of handedness?" > > > > An appropriate contrast would be [0.5 0.5 -0.5 -0.5]. > > (see > http://surfer.nmr.mgh.harvard.edu/fswiki/Fsgdf4G0V#Contrast5male-female.mtx) > > > > > Is that also true for an imbalanced design, where MaleRight and > MaleLeft consist of 15 and 5 subjects, respectively? I suspect that in > this case the above contrast would weigh MaleLeft more heavily, i.e. > each subject in this rather small subgroup would have a greater effect > on the final result. > > > > If that is true - I am wondering whether the contrast [0.75 0.25 ...] > would fix this issue, i.e. adjust for the unbalanced design. Do you > have any ideas? > > > > Best, > > Daniel > > ------------------------------------------------------------------------ > > _______________________________________________ > 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 _______________________________________________ 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.
