SPSS® 12.0 Command Syntax Reference

1510 SPCHART
Figure 3 S chart
Data Organization
For X-bar, R, or s charts, data can be organized in two ways: each case is a unit or each case
is a subgroup.
• Each case is a unit with a subgroup identifier. Cases are assigned to a category according
to the value of the identifier. Table 1 is an example of this type of data organization. The
data do not have to be sorted by subgroup. A BY variable (the subgroup identifier) is
required to sort and aggregate data and label the process variable.
• Each case is a subgroup. There are as many variables as individuals within one sample.
A sample identifier is not required. When there is one, it is used for labeling. Table 2
shows the same data as Table 1 but organized in a different way.
Table 1 Each case is a unit for X-bar, R, and s charts
Subgroup Length
8:50 6.35
11:30 6.39
8:50 6.40
11:30 6.46
8:50 6.32
11:30 6.37
8:50 6.39
11:30 6.36
... ...
Table 2 Each case is a subgroup for X-bar, R, and s charts
Subgroup N1 N2 N3 N4
8:50 6.35 6.40 6.32 6.39
11:30 6.39 6.46 6.37 6.36
... ... ... ... ...