Overview of Xpose

Xpose is an R-based model building aid for population analysis using NONMEM. It facilitates data set checkout, exploration and visualization, model diagnostics, candidate covariate identification and model comparison.

Data set checkout includes visualization of the observed variable(s), covariates and plots to reveal errors in the data file.

Model diagnostic plots includes the usual residual plots but also plots to check the validity of assumptions specific to non-linear mixed effects models.

Data exploration is also done by various plots but also includes auxiliary screening analyses such as stepwise generalized additive modeling (GAM) and tree based modeling.

The stability of the GAM results with respect to covariate model selection as well as the impact of influential individuals and certain types of covariate interactions can be explored using a bootstrap re-sampling procedure.

To facilitate documentation, Xpose can produce run summaries and run records. The run records are one page summaries of a run consisting of a combination of goodness of fit plots, parameter estimates and the model file. Run records are tabulated summaries of many runs consisting of user comments, termination messages and objective function values.

 

The Xpose development team consists of Andrew Hooker, Mats O. Karlsson and E. Niclas Jonsson. We are based at the Division of Pharmacokinetics and Drug Therapy, within the Department of Pharmaceutical Biosciences at Uppsala University.

Xpose is ©1998-2005 E. Niclas Jonsson & Mats Karlsson. ©2005-2008 Andrew C. Hooker, Justin J. Wilkins, Mats O. Karlsson and E. Niclas Jonsson. ©2009 Andrew C. Hooker, Mats O. Karlsson and E. Niclas Jonsson. All rights reserved.