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The SHEWHART Procedure


The MRCHART statement creates charts for subgroup medians and ranges, which are used to analyze the central tendency and variability of a process.

You can use options in the MRCHART statement to

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

  • tabulate subgroup sample sizes, subgroup medians, subgroup ranges, control limits, and other information

  • save control limits in an output data set

  • save subgroup sample sizes, subgroup medians, and subgroup ranges 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 the method for estimating the process standard deviation

  • specify a known (standard) process mean and 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 charts 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 of medians and ranges with the MRCHART 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.

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