Hi Bo, you can think of the Ftest as a logical 'OR' between the t-test contrasts indicated in each row. Each row is a difference of differences, so
1. (A-B)om - (A-B)pm --> Does the difference between A and B differ between groups O and P for Males?
2. (A-B)om - (A-B)qm
3. (A-C)om - (A-C)pm
4. (A-C)om - (A-C)qm
5. (A-B)of - (A-B)pf --> Does the difference between A and B differ between groups O and P for Females?
6. (A-B)of - (A-B)qf
7. (A-C)of - (A-C)pf
8. (A-C)of - (A-C)pf
I've put together the first 9 columns of the first 4 rows. The last 9 columns are all 0s. For the last for rows, the 0s and below matrix are swapped to give you the same for the females
doug
AOM BOM APM BPM AQM BQM COM CPM CQM
--------------------------------------------------------------------------
+AOM -BOM -APM -BPM 0 0 0 0 0
+AOM -BOM 0 0 -AQM +BQM 0 0 0
+AOM 0 -APM 0 0 0 -COM +CPM 0
+AOM 0 0 0 -AQM -COM 0 +CQM
On 11/17/12 9:21 PM, xiangbo_2010 wrote:
Hi Freesurfer experts,I'm very sorry to bother you, but I am very confused with the following questions:My experimental design includes three discrete factors: factor 1 with three levels (A,B,C ); factor 2 with three levels (O,P,Q); gender (F, M), and one covariate.
So I can get 18 classes: FAO, FAP,FAQ,FBO,FBP,FBQ,FCO,FCP,FCQ,MAO, MAP,MAQ,MBO,MBP,MBQ,MCO,MCP,MCQ. I want to perform the interaction between factor 1 and factor 2 regressing out the effect of gender and one covariate, but I don't know the rules for setting the contrasts for the F-test. The contrast matrix I used is:
1 1 1 -1 -1 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1 -1 0 1 -1 0 1 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1 1 1 0 0 0 -1 -1 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1 0 -1 1 0 -1 1 0 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 1 1 1 -1 -1 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 1 -1 0 1 -1 0 1 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 1 1 1 0 0 0 -1 -1 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 1 0 -1 1 0 -1 1 0 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
is it correct?
Any help will be very appreciated.
Best wishes,
Bo Xiang
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