Re: VPC with Mixture Model

Hi Mats, Could you elaborate why you would not stratify based on the subpopulations? It seems perfectly reasonable for me to simulate from the model (including random assignment of subpopulations), and then compare "apples to apples": observed subpopulation versus simulated subpopulations. In your example of 5% poor metabolizers, I would plot observed poor metabolizers (as assigned by the model) versus simulated poor metabolizers (as simulated from the model). Indeed, poor metabolizers assignment would be defined by the model, so this VPC will be conditioned on the model posthoc EST prediction, but the remaining parts of the model would be tested by this procedure. If the model is good, VPC should provide good results. It is unclear to me how sensitive this procedure is to model misspecification (in general, I think VPC is less sensitive to model misspecification than other model diagnostics) Thanks Leonid -------------------------------------- Leonid Gibiansky, Ph.D. President, QuantPharm LLC web: www.quantpharm.com e-mail: LGibiansky at quantpharm.com tel: (301) 767 5566 Mats Karlsson wrote: > Dear Satyendra, > > Interesting question. I don’t think there is much written about this, but I may be wrong. What I would not do is to try to stratify based on estimated subpopulation allocation (“EST”). Rather I would use the same VPCs as if there had been no mixture model. Possibly what you could do is be more careful in your choice of prediction intervals to display. For example, if you have a subpopulation of poor metabolizers of about 5%, displaying only median and interquartile range PIs may not be a good idea. > > Best regards, > > Mats > > Mats Karlsson, PhD > > Professor of Pharmacometrics > > Dept of Pharmaceutical Biosciences > > Uppsala University > > Box 591 > > 751 24 Uppsala Sweden > > phone: +46 18 4714105 > > fax: +46 18 471 4003 > > *From:* [email protected] [ mailto: [email protected] ] *On Behalf Of *Satyendra Suryawanshi > > *Sent:* Tuesday, April 14, 2009 6:50 PM > *To:* [email protected] > *Subject:* [NMusers] VPC with Mixture Model > > Dear all, > > I have a Mixture Model with 2 subpopulation. Now I want to check its prediction. One way to see this is a Visual Predictive Check. My question is, How to perform visual predictive check with mixture model? > > I will be thankful for your suggestion and references. > > Best regards > > Satyendra Suryawanshi, PhD > > University of Tennessee Health Science Center