Hello, 

I am starting to use FSL to preform statistical analyses. If I want to test the effect of a continuous variable (ex. age) on FA, can my design matrix be a vector with the values of age for each participant? or do I need always to specify the group of each participant? 

In this case I am using as contrasts the vectors [1] and [-1] - positive and negative effect of age on FA.


Thank you!

Best Regards, 
Beatriz