Re: repeating cases

Date: Wed, 17 Nov 1999 13:57:18 -0800 From: Lewis Sheiner <lewis@c255.ucsf.edu> Subject: Re: repeating cases The basic idea is to treat the individual as the "same" on each occasion he/she/it is encountered. This means, practically, having all records for an individual be contiguous in the data file, all with the same ID. You can restart the time scale by using a record with EVID = 3 0r 4. Different covariates do not present a problem as the $PK block recomputes the parameters at each event record. If, however, variability between occasions is envisaged, so that the person/animal is not the same between occasions, although perhaps more similar to itself on another occasion than it is to a random other individual (with the same covariate values), then you may wish to allow for both inter-individual variability (IIV) and inter-occasion (IOV) variability. You can read about how one might do this (a bit clumsily) using NONMEM in Karlsson MO, Sheiner LB: The importance of modeling inter-occasion variability in population pharmacokinetic analyses, J Pharmacokin Biopharmaceut, 21: 735-750, 1993. Good luck, LBS. PS. Note that, as happens more often, at least with human data, than one might have thought, the IOV>IIV, then treating each occaasion as though it were a distinct individual is a reasonable approximation.