SCHART Statement: SHEWHART Procedure
The SCHART statement creates an s chart for subgroup standard deviations, which is used to analyze the variability of a process.[35]
You can use options in the SCHART statement to
-
compute control limits from the data based on a multiple of the standard error of the plotted standard deviations or as probability limits
-
tabulate subgroup sample sizes, subgroup standard deviations, control limits, and other information
-
save control limits in an output data set
-
save subgroup sample sizes, subgroup means, and subgroup standard deviations in an output data set
-
read preestablished control limits from a data set
-
specify a method for estimating the process standard deviation
-
specify a known (standard) process standard deviation for computing control limits
-
display distinct sets of control limits for data from successive time phases
-
add block legends and symbol markers to reveal stratification in process data
-
superimpose stars at points to represent related multivariate factors
-
clip extreme points to make the chart more readable
-
display vertical and horizontal reference lines
-
control axis values and labels
-
control layout and appearance of the chart
You have three alternatives for producing s charts with the SCHART statement:
-
ODS Graphics output is produced if ODS Graphics is enabled, for example by specifying the ODS GRAPHICS ON statement prior to the PROC statement.
-
Otherwise, traditional graphics are produced by default if SAS/GRAPH® is licensed.
-
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.
[35] 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 (
).