Is it reasonable to add covarite to PD parameters kin or kout?

From: Li Zhao Date: July 27, 2015 technical Source: mail-archive.com
Dear NMusers, Right now I am doing covarite analysis for an indirect response model. I tested a few potential covarites and found it's STATISTICALLY significant if I add observed baseline value to kin. But I am not sure if it makes sense to add the baseline value as a covarite to kin. Could you please help me if you have had similar experiences before? Thank you very much!