SPSS® 12.0 Command Syntax Reference

Example
CREATE TICKMA = MA(TICKETS,4,2).
CREATE 313
• This example creates the series TICKMA based on centered moving average values of the
series TICKETS.
• A span of 4 is used for computing averages. At the endpoints, where four values are not
available, the average is based on the specified minimum of two values.
PMA Function
PMA creates new series based on the prior moving averages of existing series. The prior
moving average for each case in the original series is computed by averaging the values of a
span of cases preceding it.
• The specification on PMA is the name or names of the existing series and the span to be
used, in parentheses.
• Only one span can be specified and it is required. There is no default span.
• If the number of values specified for the span is not available, the case is set to systemmissing.
Thus, the number of cases with system-missing values at the beginning of the
new series equals the number specified for the span.
• When PMA encounters an imbedded missing value in the existing series, it creates two
subsets, one containing cases before the missing value and one containing cases after the
missing value. Each subset is treated as a separate series for computational purposes. The
first n cases in the second subset will be system-missing, where n is the span.
Example
CREATE PRIORA = PMA(VARA,3).
• This command creates series PRIORA by computing prior moving averages for series
VARA. Since the span is 3, the first three cases in series PRIORA are system-missing. The
fourth case equals the average of cases 1, 2, and 3 of VARA, the fifth case equals the average
of cases 2, 3, and 4 of VARA, and so on.
RMED Function
RMED produces new series based on the centered running medians of existing series.
• The specification on RMED is the name or names of the existing series and the span to be
used in finding the median, in parentheses.
• A span must be specified; there is no default.
• If the specified span is odd, RMED is naturally the middle term. If the specified span is
even, the RMED is centered by averaging each pair of uncentered medians (Velleman and
Hoaglin, 1981).
• After the initial span, a second span can be specified to indicate the minimum number of
values to use in finding the median when the number specified for the initial span is unavailable.
This makes it possible to produce nonmissing values at or near the ends of the
new series.