Dear Bill and Siwei,
Although the thought in Bill's reply is right, I think there is an error in the code. NONMEM by default uses the present values to update from the previous time. Further, it is possible to do this interpolation on the fly in the model file without changes to the data set. $INPUT ID TIME DV COV ;Cov is time-varying covariate $PK IF(NEWIND.NE.2) OTIM=0 ;initialize variable to store old time IF(NEWIND.NE.2) OCOV=0 ;initialize variable to store old covariate value $DES CCOV=OCOV IF(TIME.GT.OTIM) CCOV=OCOV+(T-TIME)*(COV-OCOV)/(TIME-OTIM) ;CCOV is linear interpolation between observed covariate values $ERROR OCOV =COV ;store previous time OTIM =TIME ;store previous time (NB haven't tested the code). Best regards, Mats Mats Karlsson, PhD Professor of Pharmacometrics Dept of Pharmaceutical Biosciences Faculty of Pharmacy Uppsala University Box 591 75124 Uppsala Phone: +46 18 4714105 Fax + 46 18 4714003 <http://www.farmbio.uu.se/research/researchgroups/pharmacometrics/> www.farmbio.uu.se/research/researchgroups/pharmacometrics/ From: owner-nmus...@globomaxnm.com [mailto:owner-nmus...@globomaxnm.com] On Behalf Of Denney, William S. Sent: 23 August 2013 20:09 To: siwei Dai; nmusers@globomaxnm.com Subject: RE: [NMusers] Time-varing covariate Hi Siwei, If you are using an algebraic model (i.e. no differential equations), then you can simply include it in your equation: e.g. assuming that SBP is systolic blood pressure in your original data set: EFF=THETA(1)+SBP*THETA(2) If you have a differential equation model and you want the time varying covariate to have an effect that is not a step change, you will need to interpolate the covariate. Within your data set, you'll need a column for the next time and the next value of the time varying covariate. Using the same assumption that you have SBP in your data set as your time varying covariate, you will want to make two new columns to allow for interpolation: ID TIME NTIME SBP NSBP DV 1 0 1 110 115 5 1 1 2 115 112 3 1 2 4 112 108 4 Then to use your parameter, you will need code like the following in your $DES section to linearly interpolate: $DES . ;; Current SBP CSBP = (NSBP - SBP)/(NTIME - TIME) * (T - TIME) + SBP . The parameter T is the current time for the differential equation solver which will be somewhere between TIME and NTIME. TIME is an important column name for NONMEM. Thanks, Bill From: owner-nmus...@globomaxnm.com [mailto:owner-nmus...@globomaxnm.com] On Behalf Of siwei Dai Sent: Friday, August 23, 2013 12:01 PM To: nmusers@globomaxnm.com Subject: [NMusers] Time-varing covariate Hi, Dear NMusers: I want to add a time-varing covariate in my model. For example, blood pressure or blood flow as covariates. But I am not sure how to do it. I see some earlier threads to discuss it but they all use complicated methods. I am wondering if there are any new way to do it in NM 7.2? I see in the user guide that EVID=4 can indicate physiological change. Is this what I should use? Thank you very much for any suggestions. Best regards, Siwei
