Dear Community,
I have an issue in re-estimating parameter values in Phoenix of a 2-CMT model that was initially developed using NONMEM.
The NONMEM model:
* 2-CMT (ADVAN3 TRANS4)
* IIV on Vc, Q, Vp and an additional baseline parameter
* No IOV
* Combined error model
* OMEGA block
* FOCE (with "INTER")
I brought everthing to Phoenix NLME using PML. I re-estimated the parameter values and I constantly obtain parameter values (robust!) which are somewhat different from the NONMEM results. The Phoenix model diagnostics in general look very good. The IPREDs of obtained with Phoenix and NONMEM are comparably good! The differences are big when comparing PRED vs. IVAR of Phoenix vs. NONMEM. I would really like to know where the differences in the estimations come from!
To give you an impression on the differences in parameter values:
NONMEM Phoenix
baseline parameter: 0.8 0.83
CL: 0.04 0.03
Vc: 4.6 27.2
Vp: 7.9 49
Q: 0.18 0.33
error add: 0.011 (variance?) 0.094 (standard deviation?)
error prop: 0.0029 (variance?) 0.095 (standard deviation?)
The OMEGA then shows more differences. Although the values of the IIVs (diagonal) are somewhat similar, the covariances are very different!
NONMEM:
positive ; IIV_Baseline
negative positive ; IIV_Vc
positive negative positive ; IIV_Q
negative positive negative positive ; IIV_Vp
Phoenix:
positive ; IIV_Baseline
positive positive ; IIV_Vc
negative positive positive ; IIV_Q
negative negative positive positive ; IIV_Vp
May be the differences come from the missing "INTER" option in Phoenix?
What could be other reasons?
Thank you very much in advance - Every thought/idea is very much appreciated!
Best
Daniel