How can I perform a semipartial correlation with two covariates?

Hello, I have fMRI functional connectivity data on which I want to test the correlation between two variables (task1 and task2 connectivity values across subjects) while controlling for the amount of 'cleaning' that was performed on the data (I have a different percentage of cleaning for task1 than for task2). I therefore thought that the correct way to control for this would be to do a semipartial correlation where I hold task1 cleaning (covariate 1) constant on the task1 connectivity values only and then task2 cleaning (covariate 2) constant on the task2 connectivity values. Can I ask how to go about performing this in matlab? Essentially it would be a semipartial correlation with two covariates but differentially holding them constant for each variable. Thank you.

Answer 1

[Jeff Miller]

Not sure if this is what you want, but maybe:

[b1,bint1,resid1] = regress(task1,covar1);  
[b2,bint2,resid2] = regress(task2,covar2);
finalans = corr(resid1,resid2);

The idea is that resid1 and resid2 are the parts of task1 and task2 scores left over after you control for the covariates, and you want to see (as I understand it) whether these left-over parts are correlated.

[Georgette Argiris]

Yes, this was exactly what I was looking for! Thank you very much Jeff!