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help > RE: Covariates in 2nd-level
Aug 31, 2014 07:08 PM | Alfonso Nieto-Castanon - Boston University
RE: Covariates in 2nd-level
Dear Jatta,
Yes, that is exactly correct. Selecting GROUP1, GROUP2, and COIL and entering the between-subject contrast [1 -1 0] will give you the desired between-group differences after correcting for potential connectivity differences between the two head-coils used.
If, in addition, you want to look at simple main effects (e.g. average connectivity in GROUP1 after discounting potential COIL differences between the two groups) you may want to "center" the covariate COIL (e.g.use [-0.3 -0.3 0.7 -0.3 -0.3 -0.3 0.7 0.7 -0.3 -0.3] instead of [1 1 2 1 1 1 2 2 1 1]) so that the zero-level of this covariate represents the "average" effect across all your subjects (note: "centering" has no effect on the original between-group differences analysis).
Hope this helps
Alfonso
Originally posted by Jatta O:
Yes, that is exactly correct. Selecting GROUP1, GROUP2, and COIL and entering the between-subject contrast [1 -1 0] will give you the desired between-group differences after correcting for potential connectivity differences between the two head-coils used.
If, in addition, you want to look at simple main effects (e.g. average connectivity in GROUP1 after discounting potential COIL differences between the two groups) you may want to "center" the covariate COIL (e.g.use [-0.3 -0.3 0.7 -0.3 -0.3 -0.3 0.7 0.7 -0.3 -0.3] instead of [1 1 2 1 1 1 2 2 1 1]) so that the zero-level of this covariate represents the "average" effect across all your subjects (note: "centering" has no effect on the original between-group differences analysis).
Hope this helps
Alfonso
Originally posted by Jatta O:
Dear Alfonso
Thank you so much for the wonderful CONN toolbox. I have found it easy to start using the toolbox with the help of the manual and this forum.
My question regards 2nd-level covariates. I have data from two group of subjects measured with two different head-coils, however the other coil was used more frequently i.e. the amount of measurements with different coils is not balanced. Both coils are used in both groups.
I would like to include the coil as a covariant in the analysis and remove its effect. I did a 2nd-level covariates GROUP1 [1111100000] and GROUP2 [0000011111] for group comparison.
Should I make a second level covariate (COIL) with subjects denoted as 1 for the other coil and 2 for the other(for example [1121112211]. Then, in the second-level analysis, when making a group comparison and controlling for the coil-effect, should I first select GROUP1, GROUP2 and COIL and the use a between-subject contrast of [1 -1 0].
Thank you in advance
Best regards
Jatta
Thank you so much for the wonderful CONN toolbox. I have found it easy to start using the toolbox with the help of the manual and this forum.
My question regards 2nd-level covariates. I have data from two group of subjects measured with two different head-coils, however the other coil was used more frequently i.e. the amount of measurements with different coils is not balanced. Both coils are used in both groups.
I would like to include the coil as a covariant in the analysis and remove its effect. I did a 2nd-level covariates GROUP1 [1111100000] and GROUP2 [0000011111] for group comparison.
Should I make a second level covariate (COIL) with subjects denoted as 1 for the other coil and 2 for the other(for example [1121112211]. Then, in the second-level analysis, when making a group comparison and controlling for the coil-effect, should I first select GROUP1, GROUP2 and COIL and the use a between-subject contrast of [1 -1 0].
Thank you in advance
Best regards
Jatta
Threaded View
Title | Author | Date |
---|---|---|
Jatta O | Aug 15, 2014 | |
Alfonso Nieto-Castanon | Aug 31, 2014 | |
Jatta O | Jan 23, 2015 | |
Alfonso Nieto-Castanon | Jan 27, 2015 | |