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PCHART Statement |
See SHWPEX4 in the SAS/QC Sample Library |
The following statements create
a SAS data set named CIRC_ONE,
which contains the number of failing circuits for 30 batches
produced by the circuit manufacturing process introduced in
the "Getting Started" section:
data circ_one; input batch fail @@; datalines; 1 7 2 6 3 6 4 9 5 2 6 11 7 8 8 8 9 6 10 19 11 7 12 5 13 7 14 5 15 8 16 13 17 7 18 14 19 19 20 5 21 7 22 5 23 7 24 5 25 11 26 4 27 6 28 3 29 11 30 3 ;
A p chart is used to monitor the proportion of failing circuits.
The following statements create the chart
shown in Output 38.4.1:
title 'Proportion of Circuit Failures'; symbol v=dot c=salmon; proc shewhart data=circ_one; pchart fail*batch / subgroupn = 500 outlimits = faillim1 outindex = 'Trial Limits' cframe = lib cinfill = bwh cconnect = salmon coutfill = yellow; run;
Batches 10 and 19 have unusually high proportions of failing circuits. Subsequent investigation identifies special causes for both batches, and it is decided to eliminate these batches from the data set and recompute the control limits. The following statements create a data set named FAILLIM2 that contains the revised control limits:
proc shewhart data=circ_one; where batch^=10 and batch^=19; pchart fail*batch / subgroupn= 500 nochart outindex ='Revised Limits' outlimits= faillim2; run; data faillims; set faillim1 faillim2; run;
The data set FAILLIMS, which contains the true and revised control limits, is listed in Output 38.4.2.
Output 38.4.2: Listing of the Data Set FAILLIMStitle 'p Chart with Revised Limits for Failed Circuits'; symbol v=dot c=salmon; proc shewhart data=circ_one limits=faillims; pchart fail*batch / subgroupn = 500 readindex = 'Revised Limits' vref = 0.0156 0.032226 vreflabels = ('Trial P' 'Trial UCL') vreflabpos = 3 lvref = 15 nolegend cframe = lib cinfill = bwh coutfill = yellow cconnect = salmon; label fail = 'Fraction Failed' batch = 'Batch Index'; run;
The READINDEX= option is used to select the revised limits displayed on the p chart in Output 38.4.3. See "Displaying Multiple Sets of Control Limits". The VREF=, VREFLABELS=, and VREFLABPOS= options are used to display and label the trial limits. You can also pass in the values of the trial limits with macro variables. For an illustration of this technique, see Example 32.6.
Output 38.4.3: p Chart with Revised Limits
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