The SCHART statement creates an chart for subgroup standard deviations, which is used to analyze the variability of a process.¹

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 charts with the SCHART statement:

• Traditional graphics are produced by default.

• ODS Graphics output is produced when you specify the ODS GRAPHICS statement prior to the PROC SHEWHART statement.

• Legacy line printer charts are produced when you specify the LINEPRINTER option in the PROC SHEWHART statement.

See Chapter 3, SAS/QC Graphics, for more information about producing these different kinds of graphs.