Dear Lucas,
for a group comparison, you would have to model a regressor for group. If you
have regressors for "group", "IV", "age", "gender" you'd have to set the
contrast weight either 1 0 0 0 or -1 0 0 0 for a t-test showing group1 >
group2 or group2 > group1 respectively, controlling for IV, age, and gender.
Good luck,
Udo
Lucas Eggert schrieb am 2009-06-27:
> Dear Donald McLaren,
> >You want [1 0 0] which is the positive effect, assuming a T-test,
> >of your IV on volume.
> >[1 1 1] is the average effect of your IV, age, and gender. This
> >would be very hard to interpret.
> Ok.
> In case, I would try a two-sample t-test to compare the gray matter
> volume between two groups, again controlling for the effect of age
> and gender,
> would the contrast be defined analogously, i.e. e.g. "1 -1 0 0"? Or
> would I do this also in a multiple regression model with an
> additional regressor 'group'? And would the
> contrast be "1 1 0 0" then (for "group", "IV", "age", "gender")?
> Thank you very much for your help!
> All the best,
> -Lucas
--
Dr. med. Dipl.-Psych. Udo Dannlowski
Cognitive Neuropsychiatry Research Group
Department of Psychiatry
University of Münster
Albert-Schweitzer-Str. 11
48149 Münster
Phone: ++49 251 8356601
Fax : ++49 251 8356612
email: [log in to unmask]
|