Design of a Central Composite (Response Surface) Experiment - Add to Design Tab

Design Considerations

Select the Add to design tab of the Design of a Central Composite (Response Surface) Experiment dialog box to access options to add points or columns to the standard design.

Add to the design

Use the options in the Add to the design group box to add points or columns to the standard design. Note that the choice of selections (i.e., adding replicates, center points) only affect the displayed design (via the Summary: Display design option on the Quick or Display design tabs). The changes will not affect the results displayed in the Correlation matrix (main effects and interactions) spreadsheet accessed via the Generators and Aliases tab (those correlations always pertain to the standard design) or in the Summary box at the top of the Design of a Central Composite (Response Surface) Experiment dialog box.

Number of genuine replicates

Enter a value in the Number of genuine replicates box to replicate the complete design the respective number of times. For example, if you enter a 1 in this box, Statistica adds one replicate to the design, resulting in two identical parts of the design. If you want to replicate selected points from the design (e.g., so that you can later obtain an estimate of pure error; see the Introductory Overview), first display the design (via the Summary: Display design option on the Quick or Display design tabs), add rows to the spreadsheet (use the Insert - Add Cases option), and then copy and paste the respective runs into those new rows.

Number of center points (per block)

Enter a value in the Number of center points box to add the respective number of center points to the design. For center point runs, all factors will be set at their center value. Note that adding center points to the design changes the axial distance Alpha for orthogonality (if the design is not blocked). Also, when the Add center points (for orthogonality & rotatability) option button is selected on the Design characteristic tab, the choice of center points in the Number of center points box is disregarded (Statistica adds as many center points as are necessary to approximate this design characteristic). Refer to the description of the design characteristic options for details concerning the relationship between the number of center points and the axial distance for orthogonality.

Number of blank columns (dep. vars).

Enter a value in the Number of blank columns box to add the respective number of blank columns to the displayed design. This option is useful if you want to print the spreadsheet with the extra columns to use as a convenient data entry form.