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

Design Considerations

Select the Quick tab of the Design of a Central Composite (Response Surface) Experiment dialog box to access options to review the design quickly as well as change factor names or values.

Summary: Display design

Click the Summary: Display design button to produce a spreadsheet specifying the settings for each experimental run. To save the design, select the spreadsheet and use the Save or Save As options via the File menu. Note that to use this spreadsheet in further analyses, you must specify it as an input spreadsheet. For more information, see the Input Spreadsheet Overview.

Order of runs

The choice of options in the Order of runs group box affects the order of runs displayed in the spreadsheet. For standard experiments, it is common practice to randomize the runs in order to avoid any systematic biases due to fluctuations in the production process across runs.

Standard order

Select the Standard order option button to display the design in standard order.

Random

Select the Random option button to randomize the order of runs.

by blocks

Select the by blocks option button to sort by blocks after randomization, resulting in randomization within blocks (if the current design is not blocked, then sorting by blocks is not available).

Change factor names, values, etc

Click the Change factor names, values, etc. button to display the Summary for Variables (Factors) spreadsheet, which contains 1) the current factor names, 2) minimum, center, and maximum values, 3) the corresponding text labels (for minimum, center, and maximum values), and 4) the text labels for the high and low star point values (i.e., Alpha, see the Introductory Overview). Type in the desired text and numeric values, and then click the OK button; the values that you entered will then be used in the spreadsheet displaying the design (option Summary: Display design, see above). See also, General User Entry Spreadsheet.

Note: Partial replications. 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 add rows to the design (use option Insert - Add Cases), and then copy and paste the respective runs into those new rows.

Anchoring of star points

Note that the star points are always "anchored" against the respective center point values. If you specify minimum, center point, and maximum factor values in the spreadsheet with the Change factor names, values, etc. option (see above), then the star point values are computed as:

center ± alpha * 1/2 * (max-min)

where center, min, and max stand for the respective center point, minimum, and maximum factor values.