Dear NMusers, I am modeling long-acting injectable formulation using transit compartment model parameterized with mtt (mean transit time) and ntr (number of transit compartment). As I would like to model multiple formulations using the same structure model, adding formulation as a categorical covariate on mtt or ntr separately decreased the OFV significantly (by ~100 units). Considering mtt and ntr are correlated parameters, should I add formulation on both mtt and ntr, or adding to either one is sufficient? Any input is greatly appreciated, Jing
PS: I am considering the latter one, due to that the simulations with changing Ktr or ntr generated similar profiles (Fig1 c and d, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3636497/pdf/psp201314a.pdf).
