Re: VPC for non-uniform sampling
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.
Quoted reply history
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: [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
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