Dear SPM users,
in my latest analysis I have two samples and I want to study the dependance of certain ROIs volume upon age.
First I checked if the two samples come from two different populations: I prepared a full factorial considering one factor (=group), one covariate (age) interacting with the factor and another covariate (scolarity) not interacting. The matrix has therefore 5 columns: in the first two there are the images (sample 1 and sample2), in the third and the fourth there is the age of the two samples (age sample 1 and age sample 2) and in the fifth there is the scolarity of all subjects.
In certain ROIs I found clusters in which there is a main effect of group and, in these clusters, volume turns out to be negatively correlated with age in both groups: the latter information comes from a separate multiple regression analysis.
Now I want to check if the slopes of the regression lines are statistically different. How should I do? I have tried creating, for instance, a contrast with 0 0 1 -1 0, but I am not sure...
Can anyone help me?
Thanks in advance,