I ran a 2 compartment model with first order absorption in Pumas and in NONMEM. I used the same initial estimates for both. However, the parameter estimates generated in Pumas are slightly different than in NONMEM and the observed concentrations vs. population prediction plot generated by pumas looks different than what I got through NONMEM (NONMEM results were more evenly distributed above and below the line of unity). I would appreciate any insight or suggestion as to what could be causing these differences.
GOF results from NONMEM
GOF results from Pumas
Parameter estimates of pumas vs. NONMEM