Visual Predictive Check (VPC) is only available for population models. In this run mode, the model is first fit with 0 iterations (regardless of the value entered for the Number of Iterations in the user interface) in order to generate the data needed to fill the standard results (such as Residuals, Theta, etc.).
Predictive Check is based on the resulting model fit estimates of Theta, sigma, and Omega. Each simulation replicate generates a dataset just like the original dataset. Both eta (individual variation) and epsilon (observation error) are sampled and used to create a population prediction. Predictive Check provides a series of summary statistics (quantiles) of the simulated data to compare with the observed data.
With Visual Predictive Check selected from the Run Mode pulldown, select the OPTIONS tab.
Except for the following, descriptions for the other options can be found in the “Simple” run mode section.
In the Seed Number field, enter an initial seed value for the random simulation instead of using a random seed.
In the Number of Replicates field, enter the number of datasets to sample for the population prediction.
The maximum number of replicates allowed is 10,000. If the user enters a larger number, only 10,000 will be generated. The value entered applies to all dependent variables.
Check the Output PRED box to include the prediction results in the PredCheckAll worksheet. If unchecked, the worksheet will only contain information for the replicates.
In the Stratify menu, select a defined categorical covariate to stratify the modeling simulation, if it is needed.
This option is available only when a categorical covariate is defined. Up to three levels of stratification are available and the same stratas are applied for all dependent variables unless they are overridden in the observed variable tab.
Click Advanced Options to show/hide available advanced options.
In the ODE Rel. Tol. field, enter the relative tolerance value for the ODE solver.
In the ODE Abs. Tol. field, enter the absolute tolerance value for the ODE solver.
In the ODE Max Step field, enter the maximum number of steps for the ODE solver.
The TABLES tab provides tools for adding simulation tables to the run.
Click the Add Table + button.
For every simulation table added here, there is a results worksheet generated.The options available for a simulation table are the same as those described in the Simple run mode “Tables” section, except for the following options:
Click Structural below the table to add the parameters defined in the model stparm statement to the Variables field.
See “Predictions and Prediction Variance Corrections” for calculation details.