XCHART Statement: CUSUM Procedure

Syntax: XCHART Statement

The basic syntax for a one-sided (decision interval) scheme using the XCHART statement is as follows:

XCHART process subgroup-variable / SCHEME=ONESIDED MU0=target DELTA=shift H=h <options> ;

The general form of this syntax is as follows:

XCHART processes subgroup-variable <(block-variables)><=symbol-variable =’character’> / SCHEME=ONESIDED MU0=target DELTA=shift H=h <options> ;

Note that the options SCHEME=ONESIDED, MU0=, DELTA=, and H= are required unless their values are read from a LIMITS= data set.

The basic syntax for a two-sided (V-mask) scheme is as follows:

XCHART process subgroup-variable / MU0=target DELTA=shift ALPHA=alpha H=h <options> ;

The general form of this syntax is as follows:

XCHART processes subgroup-variable <(block-variables)><=symbol-variable | = ’character’> / MU0=target DELTA=shift ALPHA=alpha H=h <options> ;

Note that the options MU0=, DELTA=, and either ALPHA= or H= are required unless their values are read from a LIMITS= data set.

You can use any number of XCHART statements in the CUSUM procedure. The components of the XCHART statement are described as follows.

process processes

identify one or more processes to be analyzed. The specification of process depends on the input data set specified in the PROC CUSUM statement.

If raw data are read from a DATA= data set, process must be the name of the variable containing the raw measurements. For an example, see Creating a V-Mask Cusum Chart from Raw Data.
If summary data are read from a HISTORY= data set, process must be the common prefix of the summary variables in the HISTORY= data set. For an example, see Creating a V-Mask Cusum Chart from Subgroup Summary Data.

A process is required. If more than one process is specified, enclose the list in parentheses. The parameters specified in the XCHART statement are applied to all of the processes.^[29]

subgroup-variable

is the variable that classifies the data into subgroups. The subgroup-variable is required. In the examples Creating a V-Mask Cusum Chart from Raw Data and Creating a V-Mask Cusum Chart from Subgroup Summary Data, Hour is the subgroup variable.

block-variables

are optionally specified variables that group the data into blocks of consecutive subgroups. The blocks are labeled in a legend, and each block-variable provides one level of labels in the legend. See Figure 6.12 for an example.

symbol-variable

is an optionally specified variable whose levels (unique values) determine the plotting character or symbol marker used to plot the cusums.

If you produce a line printer chart, an 'A' marks points corresponding to the first level of the symbol-variable, a 'B' marks points corresponding to the second level, and so on.
If you produce traditional graphics, distinct symbol markers are displayed for points corresponding to the various levels of the symbol-variable. You can specify the symbol markers with SYMBOLn statements.

character

specifies a plotting character for line printer charts. See Figure 6.10 for an example.

options

specify optional cusum parameters, enhance the appearance of the chart, request additional analyses, save results in data sets, and so on. The section Summary of Options, which follows, lists all options by function.

^[29]For this reason, it may be preferable to read distinct cusum parameters for each process from a LIMITS= data set.