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SPSS® 12.0 Command Syntax Reference

SPSS® 12.0 Command Syntax Reference

SPSS® 12.0 Command Syntax Reference

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Example<br />

PPLOT 1231<br />

PPLOT TICKETS<br />

/DIFF=2.<br />

• In this example, TICKETS is differenced twice before the expected and observed values<br />

are plotted.<br />

SDIFF Subcommand<br />

If the variable exhibits a seasonal or periodic pattern, you can use the SDIFF subcommand<br />

to seasonally difference the variable before plotting.<br />

• The specification on SDIFF indicates the degree of seasonal differencing and can be any<br />

positive integer.<br />

• If SDIFF is specified without a value, the degree of seasonal differencing defaults to 1.<br />

• The number of seasons plotted decreases by 1 for each degree of seasonal differencing.<br />

• The length of the period used by SDIFF is specified on the PERIOD subcommand. If the<br />

PERIOD subcommand is not specified, the periodicity established on the TSET or DATE<br />

command is used (see the PERIOD subcommand below).<br />

PERIOD Subcommand<br />

PERIOD indicates the length of the period to be used by the SDIFF subcommand.<br />

• The specification on PERIOD indicates how many observations are in one period or<br />

season. You can specify any positive integer on PERIOD.<br />

• The PERIOD subcommand is ignored if it is used without the SDIFF subcommand.<br />

• If PERIOD is not specified, the periodicity established on TSET PERIOD is in effect. If<br />

TSET PERIOD is not specified either, the periodicity established on the DATE command<br />

is used. If periodicity was not established anywhere, the SDIFF subcommand will not be<br />

executed.<br />

Example<br />

PPLOT TICKETS<br />

/SDIFF=1<br />

/PERIOD=12.<br />

• This command applies 1 degree of seasonal differencing with 12 observations per season<br />

to the variable TICKETS.<br />

LN and NOLOG Subcommands<br />

LN transforms the data using the natural logarithm (base e) to remove varying amplitude.<br />

NOLOG indicates that the data should not be log transformed. NOLOG is the default.<br />

• There are no additional specifications on LN or NOLOG.<br />

• Only the last LN or NOLOG subcommand on a PPLOT command is executed.

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