我笑着哭DX8-04F-MultifactorRSM-IVopt.docx Rev. 5/17/10
Screen tips on design evaluation graphs Exit out of the screen-tips help screen. On the floating Graphs Tool press
Contour to see where your points are located (expect these to differ somewhat from those shown below).
Standard error plot
Our points appear to be well-spaced and the choices for replication (points labeled “2”) seem reasonable. Select View, 3D Surface (or choose this off the Graphs Tool) to see the surface for standard error.
Design-Expert 8 User’s Guide D-Optimal RSM Tutorial 11
Response surface for standard error
Our design has a relatively flat surface on the standard error plot. If it was completely flat, we would get the same accuracy of predictions throughout the design space. To decrease prediction variance at any of the higher points on the plot (for example, along the constraint line), we would need to add runs in that region of the design.
Where to go from here
You are now on your own. Depending on which points Design-Expert picked for your design, you may want to add a few more runs* at the extreme vertices, along an edge, or in other locations. If you modify the design, go back and evaluate it. Check the 3D view of standard error and see how much lower it becomes at the point(s) you add. In any case, you can rest assured that, via its optimal design
capability, Design-Expert will provide a good spread of processing conditions to fit the model that you specify, and do it within the feasible region dictated by you. *We detailed how to modify the design layout in Part 2 of General One-Factor Tutorial (Advanced Features).
12 D-Optimal RSM Tutorial Design-Expert 8 User’s Guide
