This contrast will do it: [1 -1 0 0]
But I would first test [0 0 -1 1] to see if the slopes are different. If
not, then use [1 -1 0] with DOSS instead of DODS
On 12/14/2021 5:07 PM, Laura Willers de Souza wrote:
External Email - Use Caution
Yes! Sorry for that.
And I'm resending my fsgd file!
Laura.
_______________________________________________________________________________________________________________
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,
* or only for cortisol,
* or for both,
* or if the coefficient of the intercept between group and cortisol
is significant.
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
______________________________________________________________________________________________________________________
Answer by Douglas N. Greve:
Hello FreeSurfer Developers,
I want to perform an analysis of the difference between two groups
incortical thickness, having cortisol levels as covariate. This is
my model: cortical thickness ~ pathology (CU/CI) + CSFcortisol +
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?
_________________________________________________________________________________________________
Answer by Douglas N. Greve:
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]
------------------------------------------------------------------------
*De:* Douglas N. Greve <[email protected]>
*Enviado:* terça-feira, 14 de dezembro de 2021 18:54
*Para:* Laura Willers de Souza <[email protected]>
*Cc:* [email protected] <[email protected]>
*Assunto:* Re: [Freesurfer] Questions about contrasts
Can you include the previous emails in your current email?
On 12/14/2021 3:46 PM, Laura Willers de Souza wrote:
External Email - Use Caution
Dear Douglas,
Thank you so much for your answer!
Sorry, but I don't think I explained myself correctly in the previous
email.
I want to analyze the difference in cortical thickness between two
groups (CU and CI), adjusting for a covariate (cortisol CSF) and the
interaction between them.
So my model would be: cortical thickness ~ diagnosis + CSF cortisol +
diagnosis*CSF cortisol
Using the GLM DODS, the contrasts, according to the wiki example
(*MailScanner has detected a possible fraud attempt from
"secure-web.cisco.com" claiming to be*
https://surfer.nmr.mgh.harvard.edu/fswiki/Fsgdf2G1V
<https://secure-web.cisco.com/1qbucUNWhNS-2uW6Lox1w2bMK8EUHU0lm2XC7ywMcgAz1opgFdJ9TpOloRtF1uTmyVc70aldT5QkaELBu9kC0X6YiGpVUzZ3hV6ImEDrYAPF9VgAmDOudc6SysPVlhaUvzzGFirVYNLChsA_roK3faZNzYnWbdGPEJSgasor3qtQpKeAN7XvnQ4X24hWQfi35Rh8kF9yIsndHzOZGNxOdCH7U2CUMc9KxEL3N9u2-8weS-Fz01NHj2B_xMyBA8BlbS0n_wekioRXCPViGU3a_0zVQxE5Wu9sLPwFsQ3peECtbgAqHVmzWbyks9AhB3fWY/https%3A%2F%2Fsurfer.nmr.mgh.harvard.edu%2Ffswiki%2FFsgdf2G1V>),
would be:
* To verify if only the diagnosis regression coefficient is
significant (diagnosis changes cortical thickness regardless of
cortisol):
*
1 -1 0 0
*
*
To verify if the regression coefficient of the interaction
between diagnosis and cortisol is significant (the two change
cortical thickness dependently):
*
0 0 1 -1
*
*
To verify if only the cortisol regression coefficient is
significant (cortisol changes cortical thickness regardless of
diagnosis):
*
0 0 0.5 0.5
Are these contrasts corret to represent the model we designed?
Thank you so much again!
Best regards,
*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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