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SPSS® 12.0 Command Syntax Reference

SPSS® 12.0 Command Syntax Reference

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1512 SPCHART<br />

Figure 4 Individuals chart<br />

A moving range chart plots moving ranges of n successive observations on a control chart,<br />

where n is the specified span (see “SPAN Subcommand” on p. 1521). The center line is the<br />

mean of moving ranges and the control limits are calculated from the ranges, the span, and<br />

the user-specified SIGMA value (see “SIGMA Subcommand” on p. 1521). Figure 5 shows a<br />

moving range chart.<br />

Figure 5 Moving range chart<br />

Data Organization<br />

For individuals and moving range charts, data must be organized so that each case is a unit.<br />

Cases are not sorted or aggregated before plotting.<br />

Variable Specification<br />

The variable specification for I or IR subcommand is<br />

VAR [BY VAR]<br />

You must specify the process variable that contains the value for each individual observation.<br />

Each observation is plotted for the individuals chart. The range of n consecutive observations<br />

(where n is the value specified on the SPAN subcommand) is calculated and plotted for the

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