The model is actually, two independent linear models:
thicknessCU = CUOffset + CUcortisol*CUslope
thicknessCI = CIOffset + CIcortisol*CIslope

There will be four regression parameters:
[CUOffset CUslope CIOffset CIslope]

On 12/9/2021 10:48 PM, Laura Willers de Souza wrote:

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Hello FreeSurfer Developers,

I want to perform an analysis of the difference between two groups in cortical thickness, having cortisol levels as covariate.

This is my model: cortical thickness ~ pathology (CU/CI) + CSF cortisol + pathology*CSF cortisol

From the GLM DODS analysis I want to know if:

the regression coefficient is significant only for the difference between groups,

this could possibly mean two things: the difference in offset [1 -1 0 0] or the difference in slopes ([0 0 1 -1]

or only for cortisol,

[0 0 0.5 0.5] will test whether the cortisol slope is different than 0

or for both,

both what?

or if the coefficient of the intercept between group and cortisol is significant.

this does not make sense to me

Is my FSGD file (attached) correct? What would the contrasts look like?

Thanks in advance!

Laura Willers de Souza
Master Student in Biochemistry

Zimmer Lab - Federal University of Rio Grande do Sul

- Porto Alegre/RS - Brazil
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