RE: MIXTURE modeling

From: "Gobburu, Jogarao V" GOBBURUJ@cder.fda.gov Subject: RE: [NMusers] MIXTURE modeling Date: Thu, 17 Nov 2005 06:17:25 -0500 Hello, please see my responses below: 0. First of all, I am not sure what prompted you to apply a mixture model and how rich the data are. 1. You do not have to estimate different modes for the two populations for all the parameters. You should limit it to the ones that you think are reasonable, ie., you need some prior expectation (eg: poor vs fast metabolizers) or graphical evidence. 2. Covariate selection should be similar with or without MIX. However, it would be important to explore if one or several of the covariates can explain the mixture. 3. Bruce Green and Nick Holford presented some work on using log-likelihood ratios to select mixture models at the Annual AAPS meeting last week (asymptotic vs. empirical via re-randomization tests). They show that the estimation method (FO vs FOCE) makes a big difference. They may have more to add on this. Regarding volume for one of the sub-pops, do you have adequate data to estimate this parameter? Regards, Joga