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help > RE: modeling interaction with continuous predictors
Dec 22, 2021 11:12 AM | Marius Gruber
RE: modeling interaction with continuous predictors
Hello Andrew,
first of all thanks for the toolbox and also for your help here in the forum! I am using this thread from Hamed as my questions are on the same topic.
I am currently working on a study which aims to investigate the association between structural connectivity on one side and the interaction of two continuous variables x and z on the other side. We are interested in both the main effects of x and z and the interaction effect of x*z. So, after some research here on the forum, I have created the following design matrix that includes all three effects as well as several covariates. Our sample includes more than 900 subjects (MDD patients and HCs) from 3 study sites, and I z-standardized all continuous variables. For simplicity, I present only a subset of the data:
Intercept Sex Site_2 Site_3 Group_MDD Age X Z X*Z
1 0 0 0 1 0.86 -1.86 -0.83 1.56
1 1 0 0 1 0.16 1.10 1.17 1.30
1 1 0 0 0 -0.83 2.59 -0.16 -0.42
1 0 1 0 0 1.63 -0.46 -0.29 0.13
1 1 1 0 1 1.55 -1.53 -0.17 0.26
1 1 0 1 1 -1.30 -0.13 -1.17 0.15
1 0 0 1 0 -0.99 1.02 -0.37 -0.38
Test: F-test
Contrasts:
Main effect X: [0,0,0,0,0,0,1,0,0]
Main effect Y: [0,0,0,0,0,0,0,1,0]
Interaction X*Y: [0,0,0,0,0,0,0,0,1]
I have the following questions regarding these analyses:
As I understand the above posts, I can test the interaction from X and Y with this design matrix and the contrast given above. If NBS finds a network, then the structural connectivity within that network is associated with the interaction effect of X and Y. Is this correct?
Can I reliably test the simple main effects of X and Y with this design matrix and the contrasts given above, or should I create new design matrices for this that include only the variables X or Y (without their interaction)?
To ease the interpretation of the identified networks, I would perform post-hoc t-tests, using the following contrasts:
Main effect X: [0,0,0,0,0,0,1,0,0] and [0,0,0,0,0,0,-1,0,0]
Main effect Y: [0,0,0,0,0,0,0,1,0] and [0,0,0,0,0,0,0,-1,0]
Interaction X*Y: [0,0,0,0,0,0,0,0,1] and [0,0,0,0,0,0,0,0,-1]
I would use sqrt(threshold of the F-test) as the threshold in each test.
Is it possible to test these effects using the t-tests?
Thanks for your help in advance!
Best,
Marius
first of all thanks for the toolbox and also for your help here in the forum! I am using this thread from Hamed as my questions are on the same topic.
I am currently working on a study which aims to investigate the association between structural connectivity on one side and the interaction of two continuous variables x and z on the other side. We are interested in both the main effects of x and z and the interaction effect of x*z. So, after some research here on the forum, I have created the following design matrix that includes all three effects as well as several covariates. Our sample includes more than 900 subjects (MDD patients and HCs) from 3 study sites, and I z-standardized all continuous variables. For simplicity, I present only a subset of the data:
Intercept Sex Site_2 Site_3 Group_MDD Age X Z X*Z
1 0 0 0 1 0.86 -1.86 -0.83 1.56
1 1 0 0 1 0.16 1.10 1.17 1.30
1 1 0 0 0 -0.83 2.59 -0.16 -0.42
1 0 1 0 0 1.63 -0.46 -0.29 0.13
1 1 1 0 1 1.55 -1.53 -0.17 0.26
1 1 0 1 1 -1.30 -0.13 -1.17 0.15
1 0 0 1 0 -0.99 1.02 -0.37 -0.38
Test: F-test
Contrasts:
Main effect X: [0,0,0,0,0,0,1,0,0]
Main effect Y: [0,0,0,0,0,0,0,1,0]
Interaction X*Y: [0,0,0,0,0,0,0,0,1]
I have the following questions regarding these analyses:
As I understand the above posts, I can test the interaction from X and Y with this design matrix and the contrast given above. If NBS finds a network, then the structural connectivity within that network is associated with the interaction effect of X and Y. Is this correct?
Can I reliably test the simple main effects of X and Y with this design matrix and the contrasts given above, or should I create new design matrices for this that include only the variables X or Y (without their interaction)?
To ease the interpretation of the identified networks, I would perform post-hoc t-tests, using the following contrasts:
Main effect X: [0,0,0,0,0,0,1,0,0] and [0,0,0,0,0,0,-1,0,0]
Main effect Y: [0,0,0,0,0,0,0,1,0] and [0,0,0,0,0,0,0,-1,0]
Interaction X*Y: [0,0,0,0,0,0,0,0,1] and [0,0,0,0,0,0,0,0,-1]
I would use sqrt(threshold of the F-test) as the threshold in each test.
Is it possible to test these effects using the t-tests?
Thanks for your help in advance!
Best,
Marius
Threaded View
Title | Author | Date |
---|---|---|
Hamed Zivari | Dec 8, 2021 | |
Selma Lugtmeijer | Mar 10, 2022 | |
Andrew Zalesky | Mar 11, 2022 | |
Selma Lugtmeijer | Mar 11, 2022 | |
Andrew Zalesky | Mar 11, 2022 | |
Marius Gruber | Dec 22, 2021 | |
Andrew Zalesky | Dec 22, 2021 | |
Andrew Zalesky | Dec 8, 2021 | |