Hi Linda, you have two class varibles (M and F) and three continuous variables (Age, MMSE, and ED), so you'll have 2*(3+1)=8 regressors, so your contrast will have 6 elements. The order of the elements will be:
1. M-offset 2. F-offset 3. M-AgeSlope 4. F-AgeSlope 5. M-MMSE-Slope 6. F-MMSE-Slope 7. M-Ed-Slope 8. F-Ed-Slope
You are only interested in whether the MMSE changes with thickness, so you're only interested in components 5 and 6 (meaning that all others will be 0), so set your contrast to 0 0 0 0 .5 .5 0 0 The ".5 .5" means that the final value will be (0.5*M-MMSE-Slope + 0.5*F-MMSE-Slope) = average of the two slopes. The p-value will not change if you use 0 0 0 0 1 1 0 0. doug
Linda Zhang wrote:
Dear all,
I have a bit of an amateur question. I've read the slides and tutorial for group analysis, but I'm still confused about the contrasts. I made my fsgd file, which contains two groups: M and F. I also have three continuous variables: Age, MMSE, Education. I would like to test whether thickness is correlated with MMSE scores, after controlling for gender, age, and education. What should my contrast file be in this case?
Thanks for the help!
Cheers, Linda
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