If anyone has the time to open my attached model (linked below), I am having trouble with the visual predictive check for Plasma. There are 2 compounds (same type of model is being used to compare both drugs).
Could you please help me with my model to get an acceptable Visual Predictive Check for plasma. The Confidence interval bands for the lower interval are not coming up, is there a way to cheat the system due to negative observations.
If you are able to view my model, maybe you can tell me your opinion of the model diagnostics and goodness of fit plots, do they seem acceptable to you, maybe there is a problem with the type of error (multiplicative) that is giving rise to these negative plasma observations in the VPC?
Just change the multiplicative error model and put 0.01 instead of whatever you had estimated.
I tried to attach the project corrected but it did not work.
I will try again. Also change CEps to CEps1, CEps2 and CEPs3. Tp be correct, you cannot have the sane name. You would see that if you would shift to edti as texutal.
I have a similar problem. In the VPC that I did I first had an Additive error model and the Simulated 5% quantile concentrations were negative.
Then I followed your advice above changed the error model to Multiplicative and set the Stddev = 0.01. I was able to get rid off the negative values in 5% Quantile simulation.
Dose it mean I have to redo the population PK parameter estimation with a Multiplicative error model and re-estimate stddev ? I originally used an additive error model to estimate the population PK parameters.
I would greatly appreciate any advice here. Thanks!