The Regions tab (in the Define Characteristic dialog box ) displays the list of control limit regions defined for the Characteristic. The regions are numbered, starting with region1, from left to right on the chart, corresponding to the order of the data (based on date/time data entry).
Notes:
1. A Region is a continuous set of plotted data with unique control limits. The Region is defined by its first and last subgroup, indicated within the database by the subgroup’s Date/Time. (Subgroup numbers have no persistent meaning, in that they reflect only the relative position of a given subgroup within the set of subgroups indicated by the Plotted Data feature).
2. For linked data where no Date/Time field has been specified, default Date/Time stamps are applied to identify subgroups within the software. Changes to the data order or the quantity of data within earlier regions will upset the existing Region definitions, which should be edited as needed to reflect the revised data.
Initially, a Characteristic has only one region, which includes all the data (as specified in the Plotted Data tab). Regions are created from an open chart as follows:
Using the right mouse button, simply select the subgroup on the chart where a new region should begin, then select the Start New Region option in the right mouse menu. A new region will be defined on the chart whose control limits are defined using the default calculation method (see below).
A region may be deleted (removed from the chart) by selecting the region in the Subgroup Regions list box, then the Remove button. All regions (except an initial region) may be removed using the Remove All button. Removing a region has no impact on the underlying data (i.e. no data is removed or deleted).
Select a region from the Subgroup Regions list box, then select one of the following Control Limit Source options to specify the method used in defining the selected region’s control limits.
Control Limits Calculated: (Default) Select this option to use the region’s plotted subgroups for calculating the control limits.
Control Limits Fixed: Enter an UCL and a LCL (both are required). When this option is used for setting the control limits, the Normal Distribution is assumed, so that the control chart center line PCL is the midpoint of these control limits, and the sigma value used for Run Tests, Capability Indices, and the Range (or Moving Range or Sigma) chart is calculated as:
where n is subgroup size.
Note: When the UCL and LCL have been specified by the user in this manner, the Capability Indices (Cp, Cpk), Process Performance Indices (Pp, Ppk), Process Center Line (PCL) and Process Sigma are marked as Fixed in the Statistics display, since the process center line and/or process sigma values used in these statistics are calculated based on the pre-defined control limits. The Sigma Level and DPMO estimates also reflect the fixed properties of the capability analysis.
Control Limits From Other Region: Select the other region from the drop down list (which corresponds to the Subgroup Regions defined at the top of the dialog box). The control limits will be based on the calculated limits of the plotted values within the specified region, regardless of the method specified for the “based on” region.
Control Limits From Specified Subgroups: Specify a range of subgroup numbers, using the From and To text boxes. The subgroup numbers refer to the plotted order of the subgroups in this analysis, so any changes to filters applied to specify the plotted data will impact the calculation. The subgroup numbers for a given analysis may be found beneath the chart in the Statistics pane (when the Show Statistics option is checked in the chart’s right mouse menu) or in the Data Form (when the Show Data Form option is checked in the chart’s right mouse menu)