BOXCHART Statement: SHEWHART Procedure

Note: See Varying Width Box-and-Whisker Plots in the SAS/QC Sample Library.

This example shows how to create a box chart with box-and-whisker plots whose widths vary proportionately with the subgroup sample size. The following statements create a SAS data set named Times2 that contains flight departure delays (in minutes) recorded daily for eight consecutive days:

data Times2;
   label Delay = 'Delay in Minutes';
   informat Day date7. ;
   format   Day date7. ;
   input Day @ ;
   do Flight=1 to 25;
      input Delay @ ;
      output;
   end;
   datalines;
01MAR90   12  4   2   2  15   8   0  11   0   0
          0  12   3   .   2   3   5   0   6  25
          7   4   9   5  10
02MAR90   1   .   3   .   0   1   5   0   .   .
          1   5   7   .   7   2   2  16   2   1
          3   1  31   .   0
03MAR90   6   8   4   2   3   2   7   6  11   3
          2   7   0   1  10   2   5  12   8   6
          2   7   2   4   5
04MAR90  12   6   9   0  15   7   1   1   0   2
          5   6   5  14   7  21   8   1  14   3
         11   0   1  11   7
05MAR90   2   1   0   4   .   6   2   2   1   4
          1  11   .   1   0   .   5   5   .   2
          3   6   6   4   0
06MAR90   8   6   5   2   9   7   4   2   5   1
          2   2   4   2   5   1   3   9   7   8
          1   0   4  26  27
07MAR90   9   6   6   2   7   8   .   .  10   8
          0   2   4   3   .   .   .   7   .   6
          4   0   .   .   .
08MAR90   1   6   6   2   8   8   5   3   5   0
          8   2   4   2   5   1   6   4   5  10
          2   0   4   1   1
;

The following statements create the box chart shown in Output 17.4.1:

title 'Analysis of Airline Departure Delays';
proc shewhart data=Times2;
   boxchart Delay * Day /
      nohlabel
      boxstyle      = schematic
      odstitle      = title
      boxwidthscale = 1 ;
run;

The BOXWIDTHSCALE=1 option specifies that the widths of the box-and-whisker plots are to vary proportionately to the subgroup sample size n. This option is useful in situations where the sample size varies widely across subgroups. For further details, see the entry for BOXWIDTHSCALE= in Dictionary of Options: SHEWHART Procedure.