IRCHART Statement: SHEWHART Procedure

Example 15.13 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 15.11) augmented with a histogram of the weights:

ods graphics off;
title 'Individual Measurements Chart and Histogram';
proc shewhart data=Engines;
   irchart Weight*ID /
       rtmplot  = histogram
       nochart2;
run;

The chart is shown in Output 15.13.1. The RTMPLOT= option requests a histogram in the right margin. The NOCHART2 option suppresses the display of the moving range chart.

Output 15.13.1 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 Dictionary of Options: SHEWHART Procedure 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';
proc shewhart data=Engines;
   irchart Weight*ID /
       ltmplot  = schematic
       ltmargin = 8
       nochart2;
run;

The chart is shown in Output 15.13.2. 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 15.13.2 Box-and-Whisker Plot in Left Margin