XCHART Statement: SHEWHART Procedure

Overview: XCHART Statement

The XCHART statement creates an $\bar{X}$ chart for subgroup means, which is used to analyze the central tendency of a process.

You can use options in the XCHART statement to

  • compute control limits from the data based on a multiple of the standard error of the plotted means or as probability limits

  • tabulate subgroup sample sizes, subgroup means, control limits, and other information

  • save control limits in an output data set

  • save subgroup sample sizes and subgroup means in an output data set

  • read preestablished control limits from a data set

  • apply tests for special causes (also known as runs tests and Western Electric rules)

  • specify one of several methods for estimating the process standard deviation

  • specify whether subgroup standard deviations or subgroup ranges are used to estimate the process standard deviation

  • specify a known (standard) process mean and standard deviation for computing control limits

  • create a secondary chart that displays a time trend removed from the data (see Displaying Trends in Process Data)

  • 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 $\bar{X}$ charts with the XCHART 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.

Note: When working with variables data, you should analyze the variability of the process as well as its central tendency. You can use the XRCHART statement or the XSCHART statement in the SHEWHART procedure for this purpose.