Example 34.3: Displaying Distributional Plots in the Margin

IRCHART Statement

Example 34.3: Displaying Distributional Plots in the Margin

See SHWIREX3 in the SAS/QC Sample Library

You can augment a chart for individual measurements with one of several graphical displays, such as a histogram or a box-and-whisker plot. These displays summarize the measurements plotted on the chart, and, if the process is in statistical control, they provide a view of the process distribution.

For example, the following statements create an individual measurements chart for the engine weight measurements in the data set ENGINES (see Example 34.1) augmented with a histogram of the weights:

   title 'Individual Measurements Chart and Histogram';
   symbol v=dot c=yellow;
   proc shewhart data=engines;
      irchart weight*id /
          rtmplot  = histogram
          nochart2
          cconnect = yellow
          cframe   = vigb
          cboxfill = vlib
          cinfill  = vlib
          coutfill = red;
   run;

The chart is shown in Output 34.3.1. The RTMPLOT= option requests a histogram in the right margin. The NOCHART2 option suppresses the display of the moving range chart.

Output 34.3.1: Histogram in Right Margin

The following keywords, requesting different types of plots, are available with the RTMPLOT= option:

Keyword Marginal Plot

HISTOGRAM histogram

DIGIDOT digidot plot

SKELETAL skeletal box-and-whisker plot

SCHEMATIC schematic box-and-whisker plot

SCHEMATICID schematic box-and-whisker plot with outliers labeled

SCHEMATICIDFAR schematic box-and-whisker plot with far outliers labeled

See the entry for the BOXSTYLE= option in Chapter 46, "Dictionary of Options," for a description of the various box-and-whisker plots.

You can also use the LTMPLOT= option to request univariate plots in the left margin. The following statements request an individual measurements chart with a box-and-whisker plot in the left margin:

   title 'Individual Measurements Chart and Box-and-Whisker Plot';
   symbol v=dot c=yellow;
   proc shewhart data=engines;
      irchart weight*id /
          ltmplot  = schematic
          ltmargin = 8
          nochart2
          cframe   = vigb
          cconnect = yellow
          cboxfill = vlib
          idcolor  = yellow
          cinfill  = vlib
          coutfill = red;
   run;

The chart is shown in Output 34.3.2. The same keywords that are available with the RTMPLOT= option can be specified with the LTMPLOT= option. The LTMARGIN= option specifies the width (in horizontal percent screen units) of the left margin.

Output 34.3.2: Box-and-Whisker Plot in Left Margin

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*Keyword*	Marginal Plot
HISTOGRAM	histogram
DIGIDOT	digidot plot
SKELETAL	skeletal box-and-whisker plot
SCHEMATIC	schematic box-and-whisker plot
SCHEMATICID	schematic box-and-whisker plot with outliers labeled
SCHEMATICIDFAR	schematic box-and-whisker plot with far outliers labeled