Hi Anderson, thanks for your reply! It is really helpful!
But i still have some continuous questions.
2. Still, in the design that I mentioned above, if I want to test the main effect of reading ability, can i add "group" as another EV so that i can partial the effect of GROUP? the design should be like this ?
EV1: Reading Ability(Demeaned) EV2: AGE(Demeaned) EV3: SEX(Demeaned) EV4: GROUP(Demeaned)
1 0 0 0
Your reply : This would be fine if there were only 2 groups. With 3 groups, the best is to enter one EV per group, coding as 0 if not in the group, or 1 if in the group. In this case there is no need for an intercept, provided that all subjects belong to at least one group.
My question is: so should it look like this? Please check the attachment pic (RA_maineffect.png).
and when i set the contrast, should I set 4 contrasts as another pic (RA_Design) showed there?
I intended to do randomised analysis afterwards to see how RA affected DTI parameters, like FA, AD etc. Then with these four contrasts, it looks like i am just testing how RA of Group1/group2/group3/group4 affected DTI data. Then how i test the overall effect from RA to DTI data?
3. Also, if I want to test the interaction effects of RA * GROUP. can I set up the model like this:
EV1: AGE(Demeaned) EV2: GROUP(demeaned) EV3: Reading Ability (Demeaned) EV4: GROUP*Reading Ability (Demeaned)
0 0 0 1
your reply : This would be fine with only 2 groups. With 4, use the following:
EV1: Group 1 (0/1)
EV2: Group 2 (0/1)
EV3: Group 3 (0/1)
EV4: Group 4 (0/1)
EV5: Reading Ability * EV1
EV6: Reading Ability * EV2
EV7: Reading Ability * EV3
EV8: Reading Ability * EV4
EV9: Age
EV10: Sex
my question is : So it is kinda the same question with my previous one. so should i set my contrast like below?
EV1 EV2 EV3 EV4 EV5 EV6 EV7 EV8 EV9 EV10
0 0 0 0 1 0 0 0 0 0
0 0 0 0 0 1 0 0 0 0
0 0 0 0 0 0 1 0 0 0
0 0 0 0 0 0 0 1 0 0
If so, then i am also just testing the separate interaction between each group and their own RA? then how i can see the overall interaction between RA * GROUP ?
Hope my questions make sense. If there is part that confuses you, please let me know and i will try to explain more.
Thanks for your help! I really appreciate that!
Zoe ^_^
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