SCHART Statement: SHEWHART Procedure

Syntax: SCHART Statement

The basic syntax for the SCHART statement is as follows:

SCHART process $*$ subgroup-variable;

The general form of this syntax is as follows:

SCHART processes $*$ subgroup-variable <(block-variables)><=symbol-variable | ='character'> / <options >;

You can use any number of SCHART statements in the SHEWHART procedure. The components of the SCHART 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 SHEWHART 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 Standard Deviation Charts 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 Standard Deviation Charts from Subgroup Summary Data.
If summary data and control limits are read from a TABLE= data set, process must be the value of the variable _VAR_ in the TABLE= data set. For an example, see Saving Control Limits.

A process is required. If you specify more than one process, enclose the list in parentheses. For example, the following statements request distinct s charts for Weight, Length, and Width:

proc shewhart data=Measures;
   schart (Weight Length Width)*Day;
run;

subgroup-variable

is the variable that identifies subgroups in the data. The subgroup-variable is required. In the preceding SCHART statement, Day is the subgroup variable. For details, see Subgroup Variables.

block-variables

are optional 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 Displaying Stratification in Blocks of Observations for an example.

symbol-variable

is an optional variable whose levels (unique values) determine the symbol marker or character used to plot the subgroup standard deviations.

If you produce a line printer chart, an 'A' is displayed for the points corresponding to the first level of the symbol-variable, a 'B' is displayed for the 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. See Displaying Stratification in Levels of a Classification Variable for an example.

character

specifies a plotting character for line printer charts. For example, the following statements create an s chart using an asterisk (*) to plot the points:

proc shewhart data=Values lineprinter;
   schart Weight*Day='*';
run;

options

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. Dictionary of Options: SHEWHART Procedure describes each option in detail.