Example 18.2: Creating Various Styles of Box-and-Whisker Plots

The BOXPLOT Procedure

Example 18.2: Creating Various Styles of Box-and-Whisker Plots

The following example uses the flight delay data of the preceding example to illustrate how you can create box plots with various styles of box-and-whisker plots. The following statements create a plot, shown in Output 18.2.1, that displays skeletal box-and-whisker plots:

   symbol v=plus c=salmon;
   axis1 minor=none color=black label=(angle=90 rotate=0);
   title 'Analysis of Airline Departure Delays';
   title2 'BOXSTYLE=SKELETAL';

   proc boxplot data=times;
      plot delay * day /
                   boxstyle = skeletal
                   nohlabel
                   cframe   = vligb
                   cboxes   = dagr
                   cboxfill = ywh
                   vaxis    = axis1;
         label delay = 'Delay in Minutes';
   run;

In a skeletal box-and-whisker plot, the whiskers are drawn from the quartiles to the extreme values of the group. The skeletal box-and-whisker plot is the default style; consequently, you can also request this style by omitting the BOXSTYLE= option.

Output 18.2.1: BOXSTYLE=SKELETAL

The following statements request a box plot with schematic box-and-whisker plots:

   title2 'BOXSTYLE=SCHEMATIC';
   proc boxplot data=times;
      plot delay * day /
                   boxstyle  = schematic
                   nohlabel
                   cframe   = vligb
                   cboxes   = dagr
                   cboxfill = ywh
                   idcolor  = salmon
                   vaxis    = axis1;
      label delay = 'Delay in Minutes';
   run;

The plot is shown in Output 18.2.2. When BOXSTYLE=SCHEMATIC is specified, the whiskers are drawn to the most extreme points in the group that lie within the fences. The upper fence is defined as the third quartile (represented by the upper edge of the box) plus 1.5 times the interquartile range (IQR). The lower fence is defined as the first quartile (represented by the lower edge of the box) minus 1.5 times the interquartile range. Observations outside the fences are identified with a special symbol. The default symbol is a square, and you can specify the shape and color for this symbol with the IDSYMBOL= and IDCOLOR= options. Serifs are added to the whiskers by default. For further details, see the entry for the BOXSTYLE= option.

Output 18.2.2: BOXSTYLE=SCHEMATIC

The following statements create a box plot with schematic box-and-whisker plots in which the observations outside the fences are labeled:

   title2 'BOXSTYLE=SCHEMATICID';
   proc boxplot data=times;
      plot delay * day /
                   boxstyle = schematicid
                   nohlabel
                   cboxes   = dagr
                   cboxfill = ywh
                   cframe   = vligb
                   idcolor  = salmon
                   vaxis    = axis1;
      id reason;
      label delay = 'Delay in Minutes';
   run;

The plot is shown in Output 18.2.3. If you specify BOXSTYLE=SCHEMATICID, schematic box-and-whisker plots are displayed in which the value of the first ID variable (in this case, reason) is used to label each observation outside the fences.

Output 18.2.3: BOXSTYLE=SCHEMATICID

The following statements create a box plot with schematic box-and-whisker plots in which only the extreme observations outside the fences are labeled:

   title2 'BOXSTYLE=SCHEMATICIDFAR';
   proc boxplot data=times;
      plot delay * day /
                   boxstyle = schematicidfar
                   nohlabel
                   cframe   = vligb
                   cboxes   = dagr
                   cboxfill = ywh
                   idcolor  = salmon
                   vaxis    = axis1;
      id reason;
      label delay   = 'Delay in Minutes';
   run;

The plot is shown in Output 18.2.4. If you specify BOXSTYLE=SCHEMATICIDFAR, schematic plots are displayed in which the value of the first ID variable is used to label each observation outside the lower and upper far fences. The lower and upper far fences are located 3×IQR below the 25th percentile and above the 75th percentile, respectively. Observations between the fences and the far fences are identified with a symbol but are not labeled.

Output 18.2.4: BOXSTYLE=SCHEMATICIDFAR

Other options for controlling the display of box-and-whisker plots include the BOXWIDTH=, BOXWIDTHSCALE=, CBOXES=, CBOXFILL=, and LBOXES= options.

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