UCHART Statement: SHEWHART Procedure

Overview: UCHART Statement

The UCHART statement creates u charts for the numbers of nonconformities (defects) per inspection unit in subgroup samples containing arbitrary numbers of units.

You can use options in the UCHART statement to

  • specify the number of inspection units per subgroup

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

  • tabulate subgroup summary statistics and control limits

  • save control limits in an output data set

  • save subgroup summary statistics 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 a known (standard) value for the average number of nonconformities per inspection unit

  • 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 u charts with the UCHART 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.