BOXCHART Statement

Overview

The BOXCHART statement creates an $\bar{X}$ 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 32.2 and Example 32.3.1).

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

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