It is mandatory.
Y=A+bX.
Correlation: sum((Y-Ybar)*(X-Xbar))/sqrt(sum((Y-Ybar)^2)*sum((X-Xbar)^2))
When you put in a column for the mean (A), then it gets removed from X
and Y leaving you with the above equation.
Another way of looking at this is:
Sxy=sum((Y-Ybar)*(X-Xbar))/n-1
Sx^2=sum((X-Xbar)^2)/n-1
b=Sxy/Sx^2
r=b*Sx/Sy=(sum((Y-Ybar)*(X-Xbar))/n-1)/(sum((X-Xbar)^2)/n-1)*sqrt(sum((X-Xbar)^2)/n-1)/sqrt((sum((Y-Ybar)^2)/n-1)=
sum((Y-Ybar)*(X-Xbar))/sqrt(sum((X-Xbar)^2)*sqrt((sum((Y-Ybar)^2))
Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Postdoctoral Research Fellow, GRECC, Bedford VA
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Office: (773) 406-2464
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On Fri, Oct 28, 2011 at 12:21 PM, Alberto Inuggi <[log in to unmask]> wrote:
> dear FSL users
>
> suppose I want to correlate my RestState networks with some behavioural variables.
> in my GLM model (then processed by randomize, after dual regression) do i always have to put the mean regressor (a column with 1, for each subject ????).
> is this mandatory its presence in the matrix?, or if i just want to investigate my correlations can i omit it.
>
> thanks in advance
> Alberto
>
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