Dear Matt and all,
In the code you gave, DEL is a protection when F=0 as it may be in a lag-time model, not only for IWRES but also for the model as such. You can’t have a proportional error model with a prediction of zero. Add an absolute error component or switch from a lag to a transit compartment delay model are two possibilities. In general, I find IWRES useful for diagnosing the residual error model by plotting abs(IWRES) versus IPRED when I have reasonable amount of data per subject. An appropriate error model should result in a lack of trend. Others may have other ways of assuring that the residual error model is appropriate. Better alternatives are always welcome. Best regards, Mats Mats Karlsson, PhD Professor of Pharmacometrics Dept of Pharmaceutical Biosciences Uppsala University Sweden Postal address: Box 591, 751 24 Uppsala, Sweden Phone +46 18 4714105 Fax + 46 18 4714003 From: owner-nmus...@globomaxnm.com [mailto:owner-nmus...@globomaxnm.com] On Behalf Of Fidler,Matt,FORT WORTH,R&D Sent: Thursday, March 31, 2011 5:30 PM To: Nick Holford; nmusers Subject: RE: [NMusers] basic questions... Paola, I agree with Nick that there may be little use for the DEL and W variables. The standard coding may be something like: $ERROR IPRED = F IRES = DV-IPRED W = THETA(#)*F DEL = 0 IF(W.EQ.0) DEL = 1 IWRES = IRES/(W+DEL) Y = F+EPS(1)*W The W represents the “weight” of the error model. In the above example this is proportional error. The DEL is used to keep the unlikely divide by zero error from appearing when IRES/W is calculated. When W=0, IRES=RES. Like Nick, I’m don’t find too much use in this. If W = 0, I think the IWRES should be missing instead of calculated as RES. Matt. From: owner-nmus...@globomaxnm.com [mailto:owner-nmus...@globomaxnm.com] On Behalf Of Nick Holford Sent: Thursday, March 31, 2011 9:03 AM To: nmusers Subject: Re: [NMusers] basic questions... Paola, On 31/03/2011 3:02 p.m., di Gion, Paola wrote: Dear NONMEM users, as beginners in NONMEM we have the following questions: - What is the meaning of "DEL" and "W" (in the subroutine $ERROR)? They are sort of like a virus that is spread by copying and pasting from old control streams passed around among beginners. These are not standard NM-TRAN variables. Some people like to use them to create some diagnostic variables like IWRES. I find no use for them. - What is the meaning of "TOL" and when should it be used? TOL is an option for the differential equation solving subroutines (ADVAN6, ADVAN8, ADVAN9 and ADVAN13 (NM7 only). It specifies the tolerance for the numerical solution of the differential equations. A reasonable starting value is TOL=6 for NM7 (with NSIG=2 and SIGL=6). - Assumed we need to use $DES, is this possible only with NONMEM version 7 or can we use it also in NONMEM 6? You can use $DES with any version of NONMEM. It usually runs faster with NM6 than NM7. However, in some cases ADVAN13 in NONMEM7 will run faster than ADVAN6,8.9. Its hard to predict which ADVAN is best so just try different ones and use the one that runs fastest. Thanks a lot and kind regards from rainy Cologne Its raining in Cape Town too! Paola & Lisa -- Nick Holford, Professor Clinical Pharmacology Dept Pharmacology & Clinical Pharmacology University of Auckland,85 Park Rd,Private Bag 92019,Auckland,New Zealand tel:+64(9)923-6730 fax:+64(9)373-7090 mobile:+64(21)46 23 53 email: n.holf...@auckland.ac.nz http://www.fmhs.auckland.ac.nz/sms/pharmacology/holford _____ This e-mail (including any attachments) is confidential and may be legally privileged. If you are not an intended recipient or an authorized representative of an intended recipient, you are prohibited from using, copying or distributing the information in this e-mail or its attachments. If you have received this e-mail in error, please notify the sender immediately by return e-mail and delete all copies of this message and any attachments. Thank you.
