SPSS® 12.0 Command Syntax Reference

Variable Specification
SPCHART 1511
If data are organized as shown in Table 1, the variable specifications on XR and XS subcommands
are
VAR BY VAR
The variable specified before BY is the process variable, the variable that contains values for
all instances to be plotted (for example, LENGTH in Table 1). The variable specified after BY
is the category variable or the BY variable, which is the subgroup identifier (for example,
SUBGROUP in Table 1). The process variable must be numeric while the category variable
can be of any type. The chart is sorted by the category variable.
If data are organized as shown in Table 2, the variable specifications on XR and XS subcommands
are
VAR VAR [VAR...] [BY VAR]
Each of the variables specified before BY represents an instance to be plotted (for example,
N1 to N3 in Table 2). At least two variables are required and each must be numeric. Keyword
BY and the category variable (for example, SUBGROUP in Table 2) are optional; if specified,
the category variable provides labels for the category axis and can be any type of variable. If
omitted, the category axis is labeled from 1 to the number of variables specified before keyword
BY.
Example
SPCHART /TEMPLATE=’CTRL.CHT’
/XR SUBSIZE BY SHIFT.
• The data are organized as shown in Table 1. SUBSIZE is a numeric variable that measures
the part size. SHIFT contains the subgroup identifier (work shift number).
• The chart template is stored in the chart file CTRL.CHT.
I and IR Subcommands
I produces an individuals chart and IR produces an individuals and a moving range chart. Both
types are control charts for continuous variables, such as size, weight, length, and temperature.
An individuals chart plots each individual observation on a control chart. The center line
indicates the mean of all individual values and the control limits are calculated from the mean
of the moving ranges, the span, and the user-specified SIGMA value. Individuals charts are
often used with moving range charts to test process variability when the subgroup size is 1.
This occurs frequently when automated inspection and measurement technology is used and
every unit manufactured is analyzed. It also occurs when the process is so slow that a larger
subgroup size becomes impractical. Figure 4 shows an individuals chart.