help > RE: Contrast specification for Group comparison in a multi-center RCT (controlling for scanner)
Jan 13, 2021  09:01 PM | Marcel Daamen
RE: Contrast specification for Group comparison in a multi-center RCT (controlling for scanner)
Dear Till,

I wonder whether the model is overparameterized because you should only need 7 variables for dummy-coding the 8 centers/ scanners (i.e. scanner 8 implicitly specified by a "0" for all seven regressors)?

Best wishes,

Marcel


Originally posted by Till Langhammer:
Dear Alfonso and Forum members,

I would like to compare different groups. Groups are diagnosis groups in an RCT for different anxiety disorders.
We have 8 different sites and therefore different scanners.

My Model

[1 -1 0 0 0 0 0 0 0 0 0 0]

[patients controls age sex center1 center2 center3 center4 center5 center6 center7 center8]

I am not sure if this works. The results explorer and folder is named

"patients(1).controls(-1).age(0).sex(0).Dr7573199821223284"

I would have expected:

"patients(1).controls(-1).age(0).sex(0).center1(0).center2(0).center3(0).center4(0).center5(0).center6(0).center7(0).center8(0)"

I chose user defined between subject contrast and inserted [1 -1 0 0 0 0 0 0 0 0 0 0], as it is not possible to choose this contrast in the drop down menu.


How can I check if CONN calcualted the correct model?

Thanks
Till

Threaded View

TitleAuthorDate
Till Langhammer Jan 12, 2021
RE: Contrast specification for Group comparison in a multi-center RCT (controlling for scanner)
Marcel Daamen Jan 13, 2021
Till Langhammer Jan 14, 2021
Marcel Daamen Jan 14, 2021