Hi, just wondering if anyone has any advice on the following questions:
I'm using QDEC to analyze cortical thickness differences between groups and I have a few questions:
1) There are a few variables that I need to control for. First variable is scanner - I used two different scanners of different field strengths (1.5T GE and 3T Siemens) so I wanted to control for scanner. I also wanted to control for age and gender. Here's my ideal design setup:
discrete variables - groups, scanner, gender nuisance variable - age
contrast would be 1 -1 0 0 0 0
I realize that scanner, gender, and group are all discrete variables, and that age would be a continuous one. However, in the design tab, I am not able to select all 3 discrete variables (groups, scanner, and gender). Should I designate scanner or gender as a nuisance variable instead? Would it matter which one I use as the nuisance variable? Possible setup:
discrete vars - groups, scanner nuisance vars - age, gender
contrast - 1 -1 0 0 (Correct?)
2) If I use DODS, should I demean the ages if age is a nuisance variable?
3) If I use a smoothing kernel during the analysis, then create an ROI and map that ROI to each individual subject, will the resulting .stats file in each subjects stats folder reflect the smoothed data or does mapping onto each ROI just extract the raw unsmoothed data from each vertex?
Thanks! Krista