SCHART Statement: SHEWHART Procedure
Overview: SCHART Statement
The SCHART statement creates an s chart for subgroup standard deviations, which is used to analyze the variability of a process.[76]
You can use options in the SCHART statement to
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compute control limits from the data based on a multiple of the standard error of the plotted standard deviations or as probability limits
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tabulate subgroup sample sizes, subgroup standard deviations, control limits, and other information
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save control limits in an output data set
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save subgroup sample sizes, subgroup means, and subgroup standard deviations in an output data set
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read preestablished control limits from a data set
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specify a method for estimating the process standard deviation
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specify a known (standard) process standard deviation for computing control limits
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display distinct sets of control limits for data from successive time phases
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add block legends and symbol markers to reveal stratification in process data
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superimpose stars at points to represent related multivariate factors
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clip extreme points to make the chart more readable
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display vertical and horizontal reference lines
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control axis values and labels
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control layout and appearance of the chart
You have three alternatives for producing s charts with the SCHART statement:
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ODS Graphics output is produced if ODS Graphics is enabled, for example by specifying the ODS GRAPHICS ON statement prior to the PROC statement.
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Otherwise, traditional graphics are produced by default if SAS/GRAPH® is licensed.
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Legacy line printer charts are produced when you specify the LINEPRINTER option in the PROC statement.
See Chapter 3: SAS/QC Graphics, for more information about producing these different kinds of graphs.
[76] You can also use R charts for this purpose; see RCHART Statement: SHEWHART Procedure. In general, s charts are recommended with large subgroup sample sizes (
).