PCHART Statement: SHEWHART Procedure
The basic syntax for the PCHART statement is as follows:
PCHART process
subgroup-variable ;
The general form of this syntax is as follows:
PCHART processes
subgroup-variable <(block-variables)><=symbol-variable | ='character'> / <options> ;
You can use any number of PCHART statements in the SHEWHART procedure. The components of the PCHART statement are described
as follows.
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process
processes
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identify one or more processes to be analyzed. The specification of process depends on the input data set specified in the PROC SHEWHART statement.
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If numbers of nonconforming items are read from a DATA= data set, process must be the name of the variable containing the numbers. For an example, see Creating p Charts from Summary Data.
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If proportions of nonconforming items are read from a HISTORY= data set, process must be the common prefix of the summary variables in the HISTORY= data set. For an example, see Creating p Charts from Summary Data.
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If proportions of nonconforming items and control limits are read from a TABLE= data set, process must be the value of the variable _VAR_ in the TABLE= data set. For an example, see Saving Control Limits.
A process is required. If you specify more than one process, enclose the list in parentheses. For example, the following statements
request distinct p charts for Rejects and Reworks:
proc shewhart data=Measures;
pchart (Rejects Reworks)*Sample / subgroupn=100;
run;
Note that when data are read from a DATA= data set, the SUBGROUPN= option, which specifies subgroup sample sizes, is required.
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subgroup-variable
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is the variable that identifies subgroups in the data. The subgroup-variable is required. In the preceding PCHART statement, Sample is the subgroup variable. For details, see Subgroup Variables.
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block-variables
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are optional variables that group the data into blocks of consecutive subgroups. The blocks are labeled in a legend, and
each block-variable provides one level of labels in the legend. See Displaying Stratification in Blocks of Observations for an example.
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symbol-variable
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is an optional variable whose levels (unique values) determine the symbol marker or character used to plot proportions of
nonconforming items.
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If you produce a line printer chart, an 'A' is displayed for the points corresponding to the first level of the symbol-variable, a 'B' is displayed for the points corresponding to the second level, and so on.
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If you produce traditional graphics, distinct symbol markers are displayed for points corresponding to the various levels
of the symbol-variable. You can specify the symbol markers with SYMBOLn statements. See Displaying Stratification in Levels of a Classification Variable for an example.
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character
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specifies a plotting character for line printer charts. For example, the following statements create a p chart using an asterisk (*) to plot the points:
proc shewhart data=Values lineprinter;
pchart Rejects*Day='*' / subgroupn=100;
run;
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options
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enhance the appearance of the chart, request additional analyses, save results in data sets, and so on. The section Summary of Options, which follows, lists all options by function. Dictionary of Options: SHEWHART Procedure describes each option in detail.
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