Note: See Two-Way Comparative Histogram in the SAS/QC Sample Library.
Two suppliers (A and B) provide disk drives for a computer manufacturer. The manufacturer measures the disk drive opening width to compare the process capabilities of the suppliers and determine whether there has been an improvement from 1992 to 1993.
The following statements save the measurements in a data set named Disk
. There are two classification variables, Supplier
and Year
, and a format is associated with Year
.
proc format ; value mytime 1 = '1992' 2 = '1993' ; data disk; input @1 supplier $10. year width; label width = 'Opening Width (inches)'; format year mytime.; datalines; Supplier A 1 1.8932 Supplier A 1 1.8952 . . . . . . Supplier B 1 1.8980 Supplier B 1 1.8986 Supplier A 2 1.8978 Supplier A 2 1.8966 . . . . . . Supplier B 2 1.8967 Supplier B 2 1.8997 ;
The following statements create the comparative histogram in Output 5.7.1:
* Define a format for time periods; proc format ; value mytime 1 = '1992' 2 = '1993' 3 = 'Target for 1994' ; * Simulate the data; data Disk; keep Supplier Year Width; length Supplier $ 16; label Width = 'Opening Width (inches)'; format Year mytime. ; Year = 1; Supplier = 'Supplier A'; avg = 1.895 ; std = 0.0027 ; do i = 1 to 260; Width = avg + std * rannor(15535); output; end; Supplier = 'Supplier B'; avg = 1.8983 ; std = 0.0024 ; do i = 1 to 260; Width = avg + std * rannor(15535); output; end; Year = 2; Supplier = 'Supplier A'; avg = 1.8970 ; std = 0.0013 ; do i = 1 to 260; Width = avg + std * rannor(15535); output; end; Supplier = 'Supplier B'; avg = 1.8980 ; std = 0.0013 ; do i = 1 to 260; Width = avg + std * rannor(15535); output; end; run;
title "Results of Supplier Training Program"; proc capability data=Disk noprint; specs lsl = 1.8925 usl = 1.9027; comphist Width / class = ( Supplier Year ) classkey = ('Supplier A' '1993') intertile = 1.0 vaxis = 0 10 20 30 ncols = 2 nrows = 2 odstitle = title; inset cpk (4.2) / noframe pos = n; run;
The CLASSKEY= option specifies the key cell as the observations for which Supplier
is equal to 'SUPPLIER A' and Year
is equal to 2. This cell determines the binning for the other cells, and (because the NOKEYMOVE option is not specified)
the columns are interchanged so that this cell is displayed in the upper left corner. Note that if the CLASSKEY= option were
not specified, the default key cell would be the observations for which Supplier
is equal to 'SUPPLIER A' and Year
is equal to 1. If the CLASSKEY= option were not specified (or if the NOKEYMOVE option were specified), the column labeled
1992 would be displayed to the left of the column labeled 1993. See the entry for the CLASSKEY= option
for details.
The VAXIS= option specifies the tick mark labels for the vertical axis, while NROWS=2 and NCOLS=2 specify a arrangement for the tiles. The INSET statement is used to display the capability index for each cell. Output 5.7.1 provides evidence that both suppliers have reduced variability from 1992 to 1993.