RE: Poor PRED estimates

From: Leonid Gibiansky Subject:RE: [NMusers] Poor PRED estimates Date:Fri, 23 May 2003 09:36:33 -0400 Justin Looking on the WRES vs. PPED plot (slightly skewed that suggests that log-transformation may help) and OMEGAs, SIGMA below, I would agree with Mats that there is nothing really wrong with your fit. Everything looks reasonable, except too large OMEGA3 (an may be OMEGA1, but OMEGA1 describes KA, and it is reasonable for KA to have large variability). It does not mean that you cannot improve the model. I would try log transformation and FOCE INTERACTION, often they improve variability estimates. FOCE is known to give better results if OMEGAs are high (as in your case) and with the rich data (again, this is your case). Certainly, I would check whether distributions of random effects are centered around zero. If not, then again, log-transformation and FOCE could help. One the other note, if you have problems with Cmax, sometimes zero-order absorption may help to better estimate it (but you should be able to see this on the DV vs. time plot) Leonid.