Defining Sets, Specifications for Charts from Variables - R (MR, S) Tab
Select the R (MR, S) tab of the Defining Sets, Specifications for Charts from Variables dialog box to access the options described here. Use these options to define variables for control and specification limits on R, MR, or S charts. Note that set specifications are optional. If variables with chart specifications are defined, sets will automatically be created when specs change in consecutive samples.
Notes:
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.
Center line
Click the Center line button to display a standard variable selection dialog box, where you can select a variable for use as the center line on the R (MR/S) chart. The values in this variable will be used in place of the default center line.
LCL
Click the LCL button to display a standard variable selection dialog box. Select the variable that contains the values to use in computing the lower control limit for each set. You will also need to select one of the option buttons in the Specify in terms of box (see below).
Do not compute LCL by default
Select this check box to not calculate the LCL by default when a variable UCL is defined.
UCL
Click the UCL button to display a standard variable selection dialog box. Select the variable that contains the values to use in computing the upper control limit for each set. You will also need to select one of the option buttons in the Specify in terms of box (see below).
Do not compute UCL by default
Select this check box to not calculate the UCL by default when a variable LCL is defined.
Specify in terms of
You can specify control limits in terms of multiples of sigma ( 3*Sigma), as computations from probability values ( the 10th and 90th percentiles), or as a constant. Select the option button that corresponds with the data in the variable you have selected for the LCL/UCL. Note that you must use the same option for both LCL and UCL (i.e., if LCL is to be calculated as a multiple of sigma, then the UCL must also be calculated in this way).
Multiples of sigma
Select this option button if the selected variables contain values (3), that should be used in calculating the upper and lower control limits. The upper and lower control limits for each set will be calculated as ± the selected variable values * sigma.
p (normal probabilities)
Select this option button if the selected variables contain probabilities on which to base the upper and lower control limits. Note that the actual control limits will always be based on the respective normal distribution values, i.e., when establishing the control limits, the p value given in the variable will be converted to the respective normal z value, which is then applied to the computation of the control limits.
Specific value
Select this option button if the selected variables contain constants that should be treated as the lower and upper control limits for each set.
LWL
Click the LWL button to display a standard variable selection dialog box. Select the variable that contains the values to use in computing the lower warning limit for each set. You will also need to select one of the option buttons in the Specify in terms of box (see below).
Do not compute LWL by default
Select this check box to not calculate the LWL by default when a variable UWL is defined.
UWL
Click the UWL button to display a standard variable selection dialog. Select the variable that contains the values to use in computing the upper warning limit for each set. You will also need to select one of the option buttons in the Specify in terms of box (see below).
Do not compute UWL by default
Select this check box to not calculate the UWL by default when a variable LWL is defined.
Specify in terms of
You can specify warning limits in terms of multiples of sigma ( 3*Sigma), as computations from probability values (e.g., the 10th and 90th percentiles), or as a constant. Select the option button that corresponds with the data in the variables you have selected for the LWL/UWL. Note that you must use the same option for both LWL and UWL ( if LWL is to be calculated as a multiple of sigma, then the UWL must also be calculated in this way).
Multiples of sigma
Select this option button if the selected variables contain a value ( 3), that should be used in calculating the upper and lower warning limits for the sets. The upper and lower warning limits will be calculated as ± the selected variable value * sigma.
p (normal probabilities)
Select this option button if the selected variables contain probabilities on which to base the upper and lower warning limit. Note that the actual warning limits will always be based on the respective normal distribution values,(when establishing the warning limits, the p value given in the variable will be converted to the respective normal z value, which is then applied to the computation of the warning limits).