Re: VPC for non-uniform sampling

On Tue, Jan 10, 2012 at 6:09 PM, Nick Holford <[email protected]>wrote: > Simulating the data is only part of a VPC. The other part is describing > the distribution of the actual observations. If data is collected honestly > with actual sampling times then of observation times will be different for > every subject whether or not the protocol also had some random element. > > A solution to this is to bin the observed (and simulated) values around > some suitable times e.g. using nominal protocol times or with more complex > algorithms (see Lavielle et al. 2011). Then the distribution of > observations and simulations can be compared at each of those times. > > Lavielle M, Bleakley K. Automatic data binning for improved visual > diagnosis of pharmacometric models. J Pharmacokinet Pharmacodyn. > 2011;38(6):861-71. > > > > On 11/01/2012 11:44 a.m., indrajeet singh wrote: > >> you could try creating uniformly distributed time points in a new data >> set covering the whole time range in your observed data set and repeat the >> simulation for 100-200 times for 100 subjects or whatever number you think >> is reasonable for your study population size. New data set can be easily >> created in R using few lines of codes. >> >> Best >> Jeet >> >> On Tue, Jan 10, 2012 at 4:11 PM, Ayyappa Chaturvedula < >> [email protected] >> <mailto:chaturvedula_a@mercer.**edu<[email protected]>>> >> wrote: >> >> Dear expert users, >> >> I am working on a dataset where subjects were sampled at different >> visits at random. I have developed a model for the data but not >> sure how to do a VPC as they do not have the same sampling >> scheme. I appreciate some guidance in this. >> >> >> Regards, >> >> Ayyappa >> >> >> >> >> -- >> Indrajeet Singh,PhD >> Sr. Clinical Pharmacokineticist >> Abbott Labs, North Chicago, IL >> >> > -- > Nick Holford, Professor Clinical Pharmacology > Dept Pharmacology& Clinical Pharmacology, Bldg 505 Room 202D > University of Auckland,85 Park Rd,Private Bag 92019,Auckland,New Zealand > tel:+64(9)923-6730 fax:+64(9)373-7090 mobile:+64(21)46 23 53 > email: [email protected] > http://www.fmhs.auckland.ac.nz/sms/pharmacology/holford > >