The SHEWHART Procedure |

Overview |

The BOXCHART statement creates an chart for subgroup means superimposed with box-and-whisker plots of the measurements in each subgroup. Throughout this chapter, a chart of this type is referred to as a *box chart*. This chart is recommended for large subgroup sample sizes (typically greater than ten). You can also use the BOXCHART statement to create standard side-by-side box-and-whisker plots (see Example 13.2 and Example 13.3).

You can use options in the BOXCHART statement to

specify control limits for subgroup means or medians

compute control limits from the data based on a multiple of the standard error of the means (or medians) 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 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)

specify one of several methods for calculating quantile statistics (percentiles)

control the style of the box-and-whisker plots

display distinct sets of control limits for data from successive time phases

add block legends and symbol markers to reveal stratification in process data

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 box charts with the BOXCHART 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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