Hi Doug, > 3) In a group X gender X age DODS design, exactly which contrast > > (interaction) has to be examined in order to see if the analysis > > proceeds as DODS or as DOSS? And what would the course of action be > > assuming there are significant clusters for that contrast? > > group X gender X age, group X age, gender X age > > I've had statisticians tell me that you cannot do anything more if there > is a sig interaction. However, this kind of thing gets published all the > time without people even checking. If you wanted to push ahead, you have > to choose an age where you want to do the test (eg, age=0 which would be > the default or age=mean age). But you have to be aware that a sig effect > found betweeen groups will depend on the age that you test it. >
Would it not be possible to decompose such a significant interaction (e.g. group X gender X age) the same way one would decompose any ANOVA interaction, i.e. by doing a post-hoc contrast to directly compare the means corresponding to the levels of the factor of interest (e.g. group A vs group B collapsing across genders) while deciding on an acceptable value for the factors of non-interest, as you suggest for Age? Since such post-hoc comparisons cannot be done directly in QDEC, would it make sense to instead decompose the interaction by manually repeating the analysis with only the relevant factors/levels left in the design? Tudor
_______________________________________________ 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.
