Factor Levels for Recoding Factor Values
Select the User-defined high/low factor values option button on the
Design & Analysis of Central Composite (Response Surface) Experiments - Analyze Design tab (or click the adjacent 
button), or click the Review/set factor names and settings button on the
Analysis of a Central Composite (Response Surface) Experiment - Design tab to display the Factor Levels for Recoding Factor Values spreadsheet, which contains the factor low and high settings. These values are used to transform the original factor values in the computation of the Summary: Effect estimates on the
Analysis of a Central Composite (Response Surface) Experiment - ANOVA/Effects tab, and also in the computation of the Correlation matrix of design variables and Correlations of effects on the
Analysis of a Central Composite (Response Surface) Experiment - Design tab. See also General user entry spreadsheet.
Usually, when analyzing standard central composite designs, you want to rescale the original factor values so that the low and high factor settings for each factor are transformed to -1 and +1, respectively. Specifically, the values x for a factor would be transformed to x' via:
x' = (x - averagex)/[1/2 * (highx - lowx)]
This 1) enables you to interpret the effect estimates in the standard manner (i.e., as the differences between the respective factors' low and high settings), and 2) makes the effect estimates (and coefficients) for different factors comparable in size. Note that, regardless of scaling, the Regression coefficients option on the Analysis of a Central Composite (Response Surface) Experiment - ANOVA/Effects tab will always show the coefficients for the original factor settings.
When you select the User-defined high/low factor values option button on the
Design & Analysis of Central Composite (Response Surface) Experiments - Analyze Design tab (or click the adjacent button), STATISTICA first reads the data to determine default values for low and high, then displays the Factor Levels for Recoding Factor Values spreadsheet, where you can modify the low and high values for each factor. This spreadsheet is also displayed when you click the Review/set factor names and settings button on the
Analysis of a Central Composite (Response Surface) Experiment - Design tab.
- Low Value/High Value
- To change the default values, enter the respective values in the Low Value and High Value columns of the spreadsheet.
- OK
- Click the OK button to accept the values entered and return to the previous dialog box.
- Cancel
- Click the Cancel button to close the spreadsheet and return to the previous dialog box. Any changes made in the spreadsheet will be disregarded.