Link different thetas to same omega using mu referencing

Hi Consider the case where we have a categorical (potentially time-varying) covariate named CAT that can take several values (e.g. 0,1,2,3). Let's say I want to model CL depending on this categorical covariate (where parameters are estimated on log-scale). A simple solution to this would be IF(CAT.EQ.1) TVCL = THETA(1) IF(CAT.EQ.2) TVCL = THETA(2) IF(CAT.EQ.3) TVCL = THETA(3) I let CL be described by a log-normal distribution with the same omega element for all CAT values. CL = EXP(TVCL + ETA(1)) With an omega statement: $OMEGA 0.1 I now want to switch to the mu referencing framework in NONMEM. Each theta needs to be reference to a MU value, and to force it to be described by the same eta I apply the following approach. MU_1 = THETA(1) MU_2 = THETA(2) MU_3 = THETA(3) IF(CAT.EQ.1) CL = EXP(MU_1 + ETA(1)) IF(CAT.EQ.2) CL = EXP(MU_2 + ETA(2)) IF(CAT.EQ.3) CL = EXP(MU_3 + ETA(3)) With an omega statement: $OMEGA BLOCK(1) 0.1 $OMEGA BLOCK(1) SAME $OMEGA BLOCK(1) SAME where I force the omega element corresponding to ETA1, ETA2 and ETA3 to be the same. Is this a valid approach to obtain what I need? Or is there a simpler way in the mu-referencing framework to link different thetas to the same omega element? All the best, Jacob ________________________________ Confidentiality Notice: This message is private and may contain confidential and proprietary information. If you have received this message in error, please notify us and remove it from your system and note that you must not copy, distribute or take any action in reliance on it. Any unauthorized use or disclosure of the contents of this message is not permitted and may be unlawful.