I have a clarifying question about fsgd file format. We have 40 participants, and a large battery of individual difference measures (egg., vocabulary, phonological skill, etc.) We applied a PCA to the battery and found 4 components, corresponding to WMC, processing speed, comprehension ability, and phonological ability. We tested for main effects of each of these on thickness, area, and volume via QDEC. However, we also want to check for interactions - and since this is essentially 4 continuous factors, this is not QDEC-able (at least, it does not appear to be). A nuisance variable (e.g., mean thickness) is also present. Nregressors = Nclasses*(Nvariables+1) = 1*((4 components + 1 nuisance) +1) = 1*(5+1) = 6
Null contrast is 1 0 0 0 0 0
Main effect, e.g., of the working memory component (#1) is
0 1 0 0 0 0
Main effect, e.g., of the WM component modulated by the nuisance variable is
0 1 0 0 0 1
So the format to examine possible interactions, e.g., component 1 and component 2 interact to affect thickness, is
0 1 1 0 0 0
And with the nuisance variable
0 1 1 0 0 1
Do we have this right?
THANKS!!
Clint