DIFF Subcommand (PPLOT command)

DIFF specifies the degree of differencing that is used before plotting to convert a nonstationary variable into a stationary variable with a constant mean and variance.

• You can specify any positive integer on DIFF.
• If DIFF is specified without a value, the default is 1.
• The number of plotted values decreases by 1 for each degree of differencing.

Example

PPLOT VARIABLES = TICKETS
  /DIFF=2.

• In this example, TICKETS is differenced twice before the expected and observed values are plotted.