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PROC CAPABILITY and General Statements |
See CAPSPEC3 in the SAS/QC Sample Library |
In this example, the capability index C_{pk} is computed for the amplification data in AMPS. To examine the accuracy of this estimate, the following statements calculate a 90% confidence interval for C_{pk}, then display the interval on a histogram (shown in Output 1.3.1) using the INSET statement:
title 'Boosting Power of Telephone Amplifiers'; legend1 FRAME CFRAME=ligr CBORDER=black POSITION=center; proc capability data=amps noprint alpha=0.10; var decibels; spec target = 5 lsl = 4 usl = 6 ltarget = 2 llsl = 3 lusl = 4 ctarget = red clsl = yellow cusl = yellow; histogram decibels / cframe = ligr cfill = steel cbarline = white legend = legend1; inset cpklcl cpk cpkucl / header = '90% Confidence Interval' format = 6.3 cframe = black ctext = black cfill = blank; run;
The ALPHA= option in the PROC CAPABILITY statement controls the level of the confidence interval. In this case, the 90% confidence interval on C_{pk} is wide (from 0.328 to 0.496), indicating that the process may need adjustments in order to improve process variability. Confidence limits for capability indices can be displayed using the INSET statement (as shown in Output 1.3.1) or saved in an output data set using the OUTPUT statement. For formulas and details about capability indices, see "Specialized Capability Indices" . For more information about the INSET statement, see Chapter 5, "INSET Statement".
Output 1.3.1: Confidence Interval on C_{pk}ods select indices; proc capability data=amps alpha=0.10; spec target = 5 lsl = 4 usl = 6 ltarget = 2 llsl = 3 lusl = 4; var decibels; run;Output 1.3.2: Process Capability Indices
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