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help > RE: repeated measures
Aug 23, 2017 01:08 AM | Andrew Zalesky
RE: repeated measures
Hi Jay,
Case 1 looks ok now.
For case 2 (2 x 2 ANOVA with repeated measures on one factor), consider the following: Lets assume C1T1 denotes control subject 1 at time point 1 and P1T1 denotes patient 1 and time point 1. We have two main effects: patient or control (main effect 1); and time point 1 or 2 (main effect 2, repeated measured). You are interested in the interaction between these two main effects.
Design Matrix:
C1T1 0 1 1 0 0 0
C1T2 1 0 1 0 0 0
C2T1 0 1 0 1 0 0
C2T2 1 0 0 1 0 0
P1T1 0 0 0 0 1 0
P1T2 1 1 0 0 1 0
P2T1 0 0 0 0 0 1
P2T2 1 1 0 0 0 1
First column is main effect of time, 2nd column is interaction between group and time, last 4 columns are subject means.
Note that we do not model the main effect of group in the design matrix (otherwise it would be rank deficient).
Contrast (for interaction)
0 1 0 0 0 0
or: 0 -1 0 0 0 0
Exchange blocks
1 1 2 2 3 3 4 4
t-test (or you can select F-test with the first contrast)
Andrew
Originally posted by Jaykumar Grandhi:
Case 1 looks ok now.
For case 2 (2 x 2 ANOVA with repeated measures on one factor), consider the following: Lets assume C1T1 denotes control subject 1 at time point 1 and P1T1 denotes patient 1 and time point 1. We have two main effects: patient or control (main effect 1); and time point 1 or 2 (main effect 2, repeated measured). You are interested in the interaction between these two main effects.
Design Matrix:
C1T1 0 1 1 0 0 0
C1T2 1 0 1 0 0 0
C2T1 0 1 0 1 0 0
C2T2 1 0 0 1 0 0
P1T1 0 0 0 0 1 0
P1T2 1 1 0 0 1 0
P2T1 0 0 0 0 0 1
P2T2 1 1 0 0 0 1
First column is main effect of time, 2nd column is interaction between group and time, last 4 columns are subject means.
Note that we do not model the main effect of group in the design matrix (otherwise it would be rank deficient).
Contrast (for interaction)
0 1 0 0 0 0
or: 0 -1 0 0 0 0
Exchange blocks
1 1 2 2 3 3 4 4
t-test (or you can select F-test with the first contrast)
Andrew
Originally posted by Jaykumar Grandhi:
Thanks for the quick response and the
correction! I wonder why I as getting significant results
with the wrong model? I ran it again with the model you outlined
and it looks even better! I am now doing:
Case 1:
Ho: T1-T2 > 0
T1= 1 subj1subj3
T2=-1 subj2
subj1 1 1 0 0
subj2 1 0 1 0
subj3 1 0 0 1
subj1 -1 1 0 0
subj2 -1 0 1 0
subj3 -1 0 0 1
contrast 1 0 0 0
exchangeblocks 1 2 3 1 2 3
t-test
______________________________________________________
Case 2: Thanks for directing me to the 2x2 ANOVA, I think it is exactly what I am looking for. I'd like to show the difference between groups in their treatment response (T1-T2). I think what I would be looking for here is the 'interaction term' between the 2 independent variables of group and time. Would it look like this?
Case 1:
Ho: (T1-T2)gp1 - (T1-T2)gp2 > 0 ... not sure if this is how to write it
T1= 1 gp1=2 Tgp subj1subj3
T2=-1 gp2=-1 subj2
subj1 1 2 2 1 0 0
subj2 1 -1 -1 0 1 0
subj3 1 -1 -1 0 0 1
subj1 -1 2 -2 1 0 0
subj2 -1 -1 1 0 1 0
subj3 -1 -1 1 0 0 1
contrast 0 0 1 0 0 0
exchangeblocks 1 2 3 1 2 3
f-test
Thanks again!
Case 1:
Ho: T1-T2 > 0
T1= 1 subj1subj3
T2=-1 subj2
subj1 1 1 0 0
subj2 1 0 1 0
subj3 1 0 0 1
subj1 -1 1 0 0
subj2 -1 0 1 0
subj3 -1 0 0 1
contrast 1 0 0 0
exchangeblocks 1 2 3 1 2 3
t-test
______________________________________________________
Case 2: Thanks for directing me to the 2x2 ANOVA, I think it is exactly what I am looking for. I'd like to show the difference between groups in their treatment response (T1-T2). I think what I would be looking for here is the 'interaction term' between the 2 independent variables of group and time. Would it look like this?
Case 1:
Ho: (T1-T2)gp1 - (T1-T2)gp2 > 0 ... not sure if this is how to write it
T1= 1 gp1=2 Tgp subj1subj3
T2=-1 gp2=-1 subj2
subj1 1 2 2 1 0 0
subj2 1 -1 -1 0 1 0
subj3 1 -1 -1 0 0 1
subj1 -1 2 -2 1 0 0
subj2 -1 -1 1 0 1 0
subj3 -1 -1 1 0 0 1
contrast 0 0 1 0 0 0
exchangeblocks 1 2 3 1 2 3
f-test
Thanks again!
Threaded View
| Title | Author | Date |
|---|---|---|
| Jaykumar Grandhi | Aug 19, 2017 | |
| Andrew Zalesky | Aug 21, 2017 | |
| Jaykumar Grandhi | Aug 22, 2017 | |
| Andrew Zalesky | Aug 23, 2017 | |
| Jaykumar Grandhi | Sep 5, 2017 | |
| Andrew Zalesky | Sep 6, 2017 | |
| Jaykumar Grandhi | Aug 23, 2017 | |
| Andrew Zalesky | Aug 23, 2017 | |