Example 1.2: Enhancing Reference Lines

PROC CAPABILITY and General Statements

Example 1.2: Enhancing Reference Lines

See CAPSPEC1 in the SAS/QC Sample Library

A telecommunications company manufactures amplifiers to be used in telephones. Each amplifier is designed to boost the input signal by 5 decibels (dB). Since it is difficult to make every amplifier's boosting power exactly 5 decibels, the company decides that amplifiers that boost the input signal between 4 and 6 decibels are acceptable. Therefore, the target value is 5 decibels, and the lower and upper specification limits are 4 and 6 decibels, respectively. The following data set contains the boosting powers of a sample of 75 amplifiers:

   data amps;
      label decibels = 'Amplification in Decibels (dB)';
      input decibels @@;
   datalines;
   4.54 4.87 4.66 4.90 4.68 5.22 4.43 5.14 3.07 4.22
   5.09 3.41 5.75 5.16 3.96 5.37 5.70 4.11 4.83 4.51
   4.57 4.16 5.73 3.64 5.48 4.95 4.57 4.46 4.75 5.38
   5.19 4.35 4.98 4.87 3.53 4.46 4.57 4.69 5.27 4.67
   5.03 4.50 5.35 4.55 4.05 6.63 5.32 5.24 5.73 5.08
   5.07 5.42 5.05 5.70 4.79 4.34 5.06 4.64 4.82 3.24
   4.79 4.46 3.84 5.05 5.46 4.64 6.13 4.31 4.81 4.98
   4.95 5.57 4.11 4.15 5.95
   ;

The SPEC statement provides several options to control the appearance of reference lines for the specification limits and the target value. The following statements use the data set AMPS to create a histogram that demonstrates some of these options:

   title 'Boosting Power of Telephone Amplifiers';
   legend1 frame cframe=ligr cborder=black position=center;
   proc capability data=amps;
      spec  target = 5      lsl = 4         usl = 6
           ltarget = 2     llsl = 3        lusl = 4
           wtarget = 3     wlsl = 3        wusl = 3
           ctarget = red   clsl = yellow   cusl = yellow
                          cleft = vigb   cright = vigb ;
      histogram decibels / cframe = ligr
                           cfill  = bigb
                           legend = legend1;
   run;

The resulting histogram is shown in Output 1.2.1. The LTARGET=, LLSL=, and LUSL= options control the line type of the reference lines for the target, lower specification limit, and upper specification limit, respectively. Likewise, the WTARGET=, WLSL=, and WUSL= options control the line widths. The CLEFT= and PLEFT= options control the color and pattern type used to fill the area to the left of the lower specification limit. Similarly, the CRIGHT= and PRIGHT= options control the color and pattern type used to fill the area to the right of the upper specification limit.

Output 1.2.1: Controlling the Appearance of Specification Limits

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