Extrapolating a Response Surface Design


The intrepid analyst can follow the example below to extrapolate a model to factor levels beyond the ranges tested.

Take an existing design, with reasonable models and expand the optimization beyond the ranges studied.

Go to Numerical Optimization and click the options button (see below). Turn on the option to “Include Standard Error Models”.


Turning this option on creates new StdErr responses. Set the Goal(s) for the StdErr response(s) to be “in range”, and delete the lower limit. This restricts the extrapolation to have a confidence band around the prediction that is no wider than what it is at the worst run.

The factors by default have “In Range” goals with the limits set to the -1, and +1 (low and high) coded limits of the design. To extrapolate, expand the factor limits.

Set the goals for the critical responses and move to the Solutions tab, and then onto the Graphs tab.

To improve the models even further, consider building a new design with expanded ranges on the factors.

Go back to the Design node.

Go to File => Export to File… to save the design as flat file data.

Go to File => New Design… and click Yes when asked to use previous information.

Switch the design to Historical Data. Type in the number of runs from the original design.

On the factor information change the factors to be expanded.

Click (s) and then Finish without making any further changes.

Go to File => Import from File… to bring the old design back.

The old design can be copied and then pasted into the Historical Data design as well.

Save this design.

Go to Design Tools, Augment Design, Augment to open the optimal augment dialog.