as per my experience in grp analysis with cortical thickness, age and gender.....i would suggest you to use qdec and select the gender as fixed factor and age/IQ as continuous factor...once you do tht, qdec will define the contrast for you to see "correlation between thickness and age, accounting for gender"; "does avg thickness differs between female or male" AND " does thickness--age corelation differ between male and female"......
if u use qdec, there may not be need to define the contrast for your study unless your trying to use command-line mri_glmfit to do grp analysis....
lemme knw if this helps
kk
----- Original Message ----- From: mdkruepke@uwalumni.com To: "freesurfer" freesurfer@nmr.mgh.harvard.edu Sent: Wednesday, June 13, 2012 11:33:27 AM Subject: [Freesurfer] cortical thickness with a continuous variable
Freesurfers-
I am looking to investigate the whether cortical thickness varies in regards to a continues variable, while controlling for other continues variables. I am having a little trouble wrapping my head around this as i am unsure how to compare thickness in regards to a continues variable, how the contrast would look, ect. Looking at this example FSGD ( http://surfer.nmr.mgh.harvard.edu/fswiki/Fsgdf2G1V )
GroupDescriptorFile 1 Title OSGM Class Group1 Class Group2 Variables Age Input subject1 Group1 30 Input subject2 Group2 40 I am thinking i may need to randomly define two groups, and then use a contrast similar to 0 0 0.5 0.5 (contrast 4 on the same page). Which asks:
Null Hypothesis: does mean of group age slope differ from 0? Is there an average affect of age regressing out the effect of group?
Am i correct in thinking that if i use this contrast i would be able to determine whether there is a difference in cortical thickness based on any continuous variable (like age, IQ)?
Michael