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| PCHART Statement |
| See SHWPCHR in the SAS/QC Sample Library |
You can save the control limits for a p chart in a SAS data set; this enables you to apply the control limits to future data (see "Reading Preestablished Control Limits") or modify the limits with a DATA step program.
The following statements read the number of nonconforming items
per subgroup from the data set CIRCUITS (see
"Creating p Charts from Count Data" )
and save the control limits displayed in
Figure 38.2 in a data set named CIRLIM:
title 'Control Limits for the Proportion of Failing Circuits';
proc shewhart data=circuits;
pchart fail*batch / subgroupn=500
outlimits=cirlim
nochart;
run;
The OUTLIMITS= option names the data set containing the control
limits, and the NOCHART option suppresses the display of the chart.
The data set CIRLIM is listed in Figure 38.7.
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The data set CIRLIM contains one observation
with the limits for process FAIL. The variables
_LCLP_ and _UCLP_ contain the lower
and upper control limits, and the variable
_P_ contains the central line.
The value of _LIMITN_ is the nominal sample size associated
with the control limits, and the value of _SIGMAS_ is the
multiple of 
associated with the control limits.
The variables _VAR_ and _SUBGRP_ are bookkeeping variables
that save the process and subgroup-variable.
The variable _TYPE_ is a bookkeeping variable that indicates
whether the value of _P_ is an estimate
or standard value.
For more information, see "OUTLIMITS= Data Set".
You can create an output data set containing both control
limits and summary statistics with the OUTTABLE= option,
as illustrated by the following statements:
title 'Proportion Nonconforming and Control Limit Information';
proc shewhart data=circuits;
pchart fail*batch / subgroupn=500
outtable=cirtable
nochart;
run;
The data set CIRTABLE is listed in Figure 38.8.
This data set contains one observation for each subgroup sample. The variables _SUBP_ and _SUBN_ contain the subgroup proportions of nonconforming items and subgroup sample sizes. The variables _LCLP_ and _UCLP_ contain the lower and upper control limits, and the variable _P_ contains the central line. The variables _VAR_ and BATCH contain the process name and values of the subgroup-variable, respectively. For more information, see "OUTTABLE= Data Set".
An OUTTABLE= data set can be read later as a TABLE= data set. For example, the following statements read the information in CIRTABLE and display a p chart (not shown here) identical to the chart in Figure 38.2:
title 'p Chart for the Proportion of Failing Circuits';
proc shewhart table=cirtable;
pchart fail*batch;
run;
Because the SHEWHART procedure simply displays the information in a TABLE= data set, you can use TABLE= data sets to create specialized control charts (see Chapter 49, "Specialized Control Charts"). For more information, see "TABLE= Data Set".
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