Re: Time-varing covariate

> From: Mats Karlsson [email protected] > Date: Sat, 24 Aug 2013 10:02:00 +0200 > To: [email protected], [email protected], > [email protected] > Subject: RE: [NMusers] Time-varing covariate > > > 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: [email protected] [mailto:[email protected]] On > Behalf Of Denney, William S. > Sent: 23 August 2013 20:09 > To: siwei Dai; [email protected] > 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: [email protected] [mailto:[email protected]] On > Behalf Of siwei Dai > Sent: Friday, August 23, 2013 12:01 PM > To: [email protected] > 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 > > > > -------------------------------------------------------------------- > mail2web.com – Enhanced email for the mobile individual based on Microsoft® > Exchange - http://link.mail2web.com/Personal/EnhancedEmail > >