Some simple steps:
(1) Form the null hypothesis;
(2) Make it equal to 0;
(3) The contrast vector is formed from the coefficients. Any task that
isn't in the equation has a coefficient of 0.
Thus for a single column, you'd get [1 0 0] or [-1 0 0], assuming the
intercept was the last column and your first column was of interest.
Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Sat, Apr 27, 2013 at 7:27 AM, Katharina Voigt
<[log in to unmask]> wrote:
> Hello,
> I defined a GLM including the constant, and two continous covariates. I am mainly interested in the effect of the 1st covariate when controlled by the 2nd covariate. Hence, I set the contrast-value for the 1st covariate to 1 (or -1) and the contrast-value for the 2nd covariate to 0. However, SPM also requires to define a contrast-value for the intercept. At this stage I defined it as 0 (i.e. covariate of no interest (as the 2nd Cov)), however I've read/heard different opinions on this claiming to set it to 1. Hence, in that case, what does it mean setting it to 1 exactly?
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