weighting observed data

From: Franziska Schaedeli <franziska.schaedeli@mph.unibe.ch> Subject: weighting observed data Date: Mon, 05 Jun 2000 11:09:52 +0100 Dear NONMEM users, I am working on a kinetic data set from hemodialysis patients, with concentration measurements in plasma and dialysate, and with measurements of total amount excreted per observed dialysis. The study period is one week and includes three 3-hrs dialysis sessions. During these sessions, 15 to 18 dialysate concentrations were measured, whereas from plasma there are only 3 measurements available per session. Fitting these data to a PK model (individual fits) results in perfect fits for the dialysate data, whereas the plasma data fits are quite poor. I think the frequency of dialysate measurement induces a bias in the model fitting. Here is my question: Is there a way to weight the plasma data with respect to the dialysate concentration data? Bests, Franziska Schaedeli Stark