The Process role selects variables for charting.
The Sample Label role enables you to specify a variable whose values label the horizontal axis and can also identify unequal subgroup sizes. If no sample label variable is specified, the samples are identified by their subgroup sample number.
If the sample subgroups are the same size, select the Sample Size Constant option and enter the size in the text box. If you entered a Sample Label variable, its values are used to label the horizontal axis. The sample size is used in the calculation of the limits regardless of whether the samples have missing values.
If the sample subgroups have an unequal number of rows or have missing values and you have a column identifying each sample, select the Sample Grouped by Sample Label option and enter the sample identifying column as the sample label.
For attribute charts (p-, np-, c-, and u-charts), this variable is the subgroup sample size. Additional options appear on the launch window, including Sample Size, Constant Size, and/or Unit Size, depending on your selection. In variables charts, it identifies the sample. When the chart type is IR, a Range Span text box appears. The range span specifies the number of consecutive measurements from which the moving ranges are computed.
The illustration in Variables Charts with Unequal Subgroup Sample Sizes shows an X-chart for a process with unequal subgroup sample sizes, using the sample data from the Quality Control sample data folder.
Variables Charts with Unequal Subgroup Sample Sizes
The Phase role enables you to specify a column identifying different phases, or sections. A phase is a group of consecutive observations in the data table. For example, phases might correspond to time periods during which a new process is brought into production and then put through successive changes. Phases generate, for each level of the specified Phase variable, a new sigma, set of limits, zones, and resulting tests.
On the window for X-, R-, S-, IR-, P-, NP-, C-, U-, Presummarize, and Levey-Jennings charts, a Phase variable button appears. If a phase variable is specified, the phase variable is examined, row by row, to identify to which phase each row belongs. Saving to a limits file reveals the sigma and specific limits calculated for each phase. See Phase Example for an example.
The By role identifies a variable to produce a separate analysis for each value that appears in the column.

Help created on 9/19/2017