Re: [mixture models] assign individual to a subpopulation every dosing record?

On 8/27/2014 12:21 PM, Jiang, Yu wrote: > Dear Lenonid, > > Thank you for your suggestion! That is very helpful. But I am not sure how to > implement this in NONMEM. I might be wrong, but from my understanding, the > $MIX block only deals with assigning subpopulation to an individual. But in my > case I need to assign states to each occasion of a given individual first. > Could you maybe be a little more specific on how to do the coding to evaluate > the states from occasion to occasion? > > Thanks, > > Yu > > Graduate student in Clinical Pharmaceutical Science > > University of Iowa > ________________________________________ > From: Leonid Gibiansky [[email protected]] > Sent: Tuesday, August 26, 2014 2:14 PM > To: Jiang, Yu; [email protected] > Subject: Re: [NMusers] [mixture models] assign individual to a subpopulation > every dosing record? > > Yu, > In terms of coding, you can do it using 4 sub-populations: > > KA1-KA1 > KA1-KA2 > KA2-KA1 > KA2-KA2 > > Interpretation would be quite complicated as you would need to assume > that each subjects can be in two states, KA1 and KA2, and this state may > change from occasion to occasion. > > For consistency, you may need to assume that each subject can be in KA1 > state with the probability f1, and in KA2 state with the probability > f2=1-f1, and then fractions of the four sub-populations defined above > would be expressed as > P1=f1*f1 > P2=f1*f2 > P3=f2*f1 > P4=f2*f2 > > Alternatively, you may want to stay with just one population (same > population KA for all subjects) but allow high inter-occasion variability. > > Leonid > > -------------------------------------- > Leonid Gibiansky, Ph.D. > President, QuantPharm LLC > web: www.quantpharm.com > e-mail: LGibiansky at quantpharm.com > tel: (301) 767 5566 > > On 8/26/2014 1:43 PM, Jiang, Yu wrote: > > > Dear NMusers, > > > > I am currently trying to use mixture models on my data because the > > absorption rate constant (Ka) appears to follow a bi-modal distribution. > > But what makes this complicated is that each subject has two dosing > > occasions with a washout period in between, and the absorption tends to > > vary a lot for the same individual (the extent of inter occasion > > variability of Ka is similar between individual variability). Therefore > > I would like to allow Ka to vary for the same subject during different > > occasions while keeping all the other parameters the same for a certain > > subject. I know I could use inter-occasion eta term on Ka, but I want to > > allow Ka to have the ability to be assigned to different subpopulations > > for the same individual. But in the mixture model structure, the $MIX is > > called once per individual and we can only assign each individual to a > > subpopulation once.. I wonder if there is a way to assign individual to > > a subpopulation every dosing record? > > > > Thank you in advance. I appreciate any comments or suggestions. > > > > Yu > > > > Graduate student in Clinical Pharmaceutical Science > > > > University of Iowa > > > > No virus found in this message. > > Checked by AVG - www.avg.com http://www.avg.com > > Version: 2014.0.4716 / Virus Database: 4007/8104 - Release Date: 08/26/14 > > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2014.0.4716 / Virus Database: 4007/8110 - Release Date: 08/27/14