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Hello SPM community!
My study has 2 groups: high risk (n=33) and low risk subjects (n=36). I have a contrast map looking at the effects of a stimulus versus rest.
At the 2nd level of analyses, I want to do an independent samples t-test, with group 1 being high risk and group 2 being low risk.
I have 3 covariates: gender (0=male, 1=female), anxiety levels (range of 0-25 based on a questionnaire), lifetime number of drugs used (range of 0-500 based on self-report).
How do I add in a covariate?
Do I create a separate covariate module with one text file per covariate?
Example:
module/textfile 1: gender noted as 0 or 1 (n=69)
module/textfile 2: anxiety levels (n=69)
module/textfile 3: drugs (n=69)
Or do I have to create a module for each group per corvariate?
Example:
module/textfile 1: high risk gender (n=33)
module/textfile 2: low risk gender (n=69)
Also, how could I look at the complex interaction effect of gender*anxiety or gender*anxiety*drugs?
Thank you in advance!
Maria