I would like to see if the difference in the number of BPD symptoms from baseline to follow-up two years later can predict psychosocial functioning at the 2 year follow-up. So I wanted to do a linear regression using a difference score (BPD score T1- BPD score T2) as the IV and different measures of functioning at T2 as the DV's (e.g. SOFAS score as global functioning; peer rating scale as interpersnal functioning; and some binary measures such as work or no work at T2; so will need to complete a series of regressions).
Is it valid to use the difference score. I have read a lot about using a difference score as a dependent variable but am unsure if the same information would correspond to using a difference score as a IV?
I guess an additional question would be is it more approriate to use T1 measures of the outcome variables as covariates in the regression equation in order to measure change in that variable also? Or is that a seperate question?
I appreciate any comments as I am quiet unsure of how to proceed and am going around in circles in how best to get some clarity.