Re: Very small P-Value for ETABAR

Jian, ETABAR p-value could be a useful quick check of the results, but it should not be used to replace the graphical evaluation of the model. Graphical evaluation should always include the histograms of the random effects, QQ plot of the random effects versus standard normal distribution, scatter plot matrix that visualizes correlation of the random effects, and plots of random effects versus all important (or all available) continuous and categorical covariates (as box-plots for categorical). These visual checks are much more powerful tools to detect a problem than ETABAR p-values. If they are OK than I would not worry about ETABAR. However, small ETABAR p-value often hints that the ETA distribution is not symmetric, or has outliers (non-symmetric long tails). Thanks Leonid -------------------------------------- Leonid Gibiansky, Ph.D. President, QuantPharm LLC web: www.quantpharm.com e-mail: LGibiansky at quantpharm.com tel: (301) 767 5566 Jian Xu wrote: > Dear NMUSERS, > > A few years back, there was a discussion on the P-value for ETABAR. However, I am not sure how to appropriately handle very small P-value(s) for ETABAR situation during the development of a model. I need some clarifications to a few questions: > > 1: Should we just ignore this small P-Value warning? > > 2: Can we change IIV model to avoid small P-value for ETABAR? Or any other suggestions? > > 3: Does NONMEM make any assumptions on ETA distribution? > > This P-value for ETABAR really bugs me a lot. I look forward to seeing some input. Thank you and I appreicate your time and help. Jian