The Initial Estimates panel allows typing or mapping initial values and lower and upper boundaries for different indirect response parameters.
Note: Multiple-dose datasets require that initial parameter values be supplied. For more on setting initial parameter estimates, see the “Parameter Estimates and Boundaries Rules” section.
If initial estimates and parameter boundaries for ASCII models are not set in the code, then they must be set in the Initial Estimates panel.
In datasets containing multiple sort variables, the initial estimates must be provided for each level of the sort variables unless the Propagate Final Estimates checkbox is selected. Checking this box applies the same types of parameter calculations and boundaries to all sort levels. Required input is highlighted orange in the interface.
If multiple sort variables have been mapped in the Main Mappings panel, the Select sorts dialog is displayed so that the sort variables to include in the internal worksheet can be selected.
None: Columns mapped to this context are not included in any analysis or output.
Sort: Categorical variable(s) identifying individual data profiles.
Parameter: Model parameters such as v (volume) or km (Michaelis constant).
Initial: Initial parameter estimate values.
Fixed or Estimated: For Dissolution models. Whether the initial parameter is fixed or estimated.
Lower: Lower parameter boundary.
Upper: Upper parameter boundary.
The lower and upper values limit the range of values the parameters can take on during model fitting. This can be very valuable if the parameter values become unrealistic or the model will not converge. Although bounds are not always required, it is recommended that Lower and Upper bounds be used routinely. If they are used, every parameter must be given lower and upper bounds.
The Phoenix default bounds are zero for one bound and ten times the initial estimate for the other bound. For models with parameters that may be either positive or negative, user-defined bounds are preferred.
Note: For the WinNonlin Generated Initial Parameter Values option with Dissolution models, to avoid getting pop-up warnings that “WinNonlin will determine initial estimate” when using the Initial Estimates internal worksheet setup, delete the initial values and change the menu option from Estimated to Fixed before entering the initial estimates. Once the dropdown is changed from Fixed to Estimated, the initial value entered cannot be deleted and the warning pop-up will be displayed. Note that this situation does not affect the estimation process, as the entered initial value will not be used and WinNonlin will estimate the initial value as requested.
When using an internal worksheet, press Rebuild to reset the worksheet to its default state and delete all entered values.
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