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help > RE: Design matrix and contrast for 2 way ANOVA, and f-value
Dec 7, 2019 07:12 AM | Andrew Zalesky
RE: Design matrix and contrast for 2 way ANOVA, and f-value
Hi Davide,
Using 0/1 or -1/1 to model the condition effect will give the same result with respect to the interaction term. Try it.
For the main effect of group, a repeated measures design is not required. I.e. the individual's group status will remain the same for both measurements. Therefore, you might want to first average the connectivity matrices across the two conditions when testing for the effect of group.
The first design is fine, but it does not capitalize on the repeated measures design of your experiment.
Andrew
Originally posted by davideit7:
Using 0/1 or -1/1 to model the condition effect will give the same result with respect to the interaction term. Try it.
For the main effect of group, a repeated measures design is not required. I.e. the individual's group status will remain the same for both measurements. Therefore, you might want to first average the connectivity matrices across the two conditions when testing for the effect of group.
The first design is fine, but it does not capitalize on the repeated measures design of your experiment.
Andrew
Originally posted by davideit7:
Hi Andrew,
thanks for the very quick reply.
Yes, sorry distraction mistake. To be faster I've copied and pasted the interaction column from the placebo group to the drugs group without paying attention to the switch of sign in the previous columns.
Regarding to model the repeated measure,the matrix then would be (I'm modelling a situation with 4 subjects 2 for group (P = placebo; D = drugs), and 2 condition A and B)
as you suggested: first column would represent the conditions, second column represent interaction, and then 1 column for each subject. However I have some doubt:
1- regarding the column for the subjects, for the treament group I've used -1 is it correct? Otherwise I was wondering how can I differenciated between the 2 treatment group?
2- Considering using "t-test" what would be now the contrast?
Is not clear to me what would be the contrast to test if there's a main effect of the treatment.
3- regarding the first desing (2nd column treatment, 3rd condition, 4th interaction)
I suppose the results are going to be different compare with the other model. Which solution would you suggest?
I'm sorry for the naive questions but my experience with the GLM is zero, I've just started to approach it.
Thanks again for the attention.
Davide
thanks for the very quick reply.
Yes, sorry distraction mistake. To be faster I've copied and pasted the interaction column from the placebo group to the drugs group without paying attention to the switch of sign in the previous columns.
Regarding to model the repeated measure,the matrix then would be (I'm modelling a situation with 4 subjects 2 for group (P = placebo; D = drugs), and 2 condition A and B)
1-P_A 1 1 1
0 0 0
1-P_B -1 -1 1 0
0 0
2-P_A 1 1 0
1 0 0
2-P_B -1 -1 0 1
0 0
3-D_A 1 -1 0 0
-1 0
3-D_B -1 1 0 0
-1 0
4-D_A 1 -1 0
0 0 -1
4-D_B -1 1 0
0 0 -1
as you suggested: first column would represent the conditions, second column represent interaction, and then 1 column for each subject. However I have some doubt:
1- regarding the column for the subjects, for the treament group I've used -1 is it correct? Otherwise I was wondering how can I differenciated between the 2 treatment group?
2- Considering using "t-test" what would be now the contrast?
1/-1 0 0 0 0 0 0 0 to test whether
there's a main effect of condition A or B?
0 1/-1 0 0 0 0 0 0 to test whether
there's an interaction?
Is not clear to me what would be the contrast to test if there's a main effect of the treatment.
3- regarding the first desing (2nd column treatment, 3rd condition, 4th interaction)
1-P_A 1 1 1 1
1-P_B 1 1 -1 -1
2-P_A 1 1 1 1
2-P_B 1 1 -1 -1
3-D_A 1 -1 1 -1
3-D_B 1 -1 -1 1
4-D_A 1 -1 1 -1
4-D_B 1 -1 -1 1
I suppose the results are going to be different compare with the other model. Which solution would you suggest?
I'm sorry for the naive questions but my experience with the GLM is zero, I've just started to approach it.
Thanks again for the attention.
Davide
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Title | Author | Date |
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Woomi Ban | May 30, 2019 | |
davideit7 | Dec 5, 2019 | |
Andrew Zalesky | Dec 6, 2019 | |
davideit7 | Dec 6, 2019 | |
Andrew Zalesky | Dec 7, 2019 | |
davideit7 | Jan 20, 2020 | |
Andrew Zalesky | Jan 21, 2020 | |
davideit7 | Jan 22, 2020 | |
Andrew Zalesky | Jan 23, 2020 | |
Woomi Ban | Jun 10, 2019 | |
Andrew Zalesky | Jun 10, 2019 | |
Andrew Zalesky | Jun 1, 2019 | |