Defining Sets, Specifications for Charts from Variables

Click the Chart specs vars for sets button on the

tab to display the Defining Sets, Specifications for Charts from Variables dialog box. Use the options in this dialog box to define variables for control and specification limits. Note that set specifications are optional. If variables with chart specifications are defined, sets will automatically be created when specs change in consecutive samples. This dialog box contains two tabs: X(X-Bar) and R (MR, S).

Missing values in specification variables

In Statistica, a change in a specification variable value (e.g., an increase in the UCL for the range) is used to signal the start of a new set. If there are missing data within a specification variable ( the specification variable for the Range UCL is missing observations), it is not known to which set the sample should be assigned. Therefore in order to avoid incorrect or seemingly incorrect results when missing data are encountered in the specification variable, an error message is displayed and the chart is not created.

Specifying sigma

For any chart there can only be one estimate of sigma; however, there are various chart elements that are functions of sigma [ such as the center line of the range chart; sigma is a function of the center line for the range]. Therefore, if you define sigma, the center line for the range chart is automatically defined, and vice versa. Thus, only one of these specifications for sigma can be set. For example, if you specify a center line for the range chart on the

R (MR, S)

tab, and then specify a value for process sigma on the

X (X-bar)

tab, the variable setting for the range chart center line will automatically be cleared.

OK

Click the OK button to accept the changes you have made and return to the Defining Variables dialog box.

Cancel

Click the Cancel button to close this dialog box without accepting any changes.

Clear all

Click the Clear all button to clear all the selections made on both tabs of this dialog box. All specifications will be set to none.