The TIMEDATA Procedure (Experimental)

Accumulation

Boundary Alignment

If the ACCUMULATE= option in the ID or VAR statement is specified, data set observations are accumulated within each time period. The frequency (width of each time interval) is specified by the INTERVAL= option in the ID statement. The ID variable contains the time ID values. Each time ID value corresponds to a specific time period. Accumulation is useful when the input data set contains transactional data, whose observations are not spaced with respect to any particular time interval. The accumulated values form the time series, which is used in subsequent analyses.

For example, suppose a data set contains the following observations:

   19MAR1999    10
   19MAR1999    30
   11MAY1999    50
   12MAY1999    20
   23MAY1999    20

If the INTERVAL=MONTH is specified, all of the preceding observations fall within a three-month period of time between March 1999 and May 1999. The observations are accumulated within each time period as follows:

If the ACCUMULATE=NONE option is specified, an error is generated because the ID variable values are not equally spaced with respect to the specified frequency (MONTH).

If the ACCUMULATE=TOTAL option is specified, the resulting time series is:

   O1MAR1999    40
   O1APR1999    .
   O1MAY1999    90

If the ACCUMULATE=AVERAGE option is specified, the resulting time series is:

   O1MAR1999    20
   O1APR1999    .
   O1MAY1999    30

If the ACCUMULATE=MINIMUM option is specified, the resulting time series is:

   O1MAR1999    10
   O1APR1999    .
   O1MAY1999    20

If the ACCUMULATE=MEDIAN option is specified, the resulting time series is:

   O1MAR1999    20
   01APR1999    .
   O1MAY1999    20

If the ACCUMULATE=MAXIMUM option is specified, the resulting time series is:

   O1MAR1999    30
   O1APR1999    .
   O1MAY1999    50

If the ACCUMULATE=FIRST option is specified, the resulting time series is:

   O1MAR1999    10
   O1APR1999    .
   O1MAY1999    50

If the ACCUMULATE=LAST option is specified, the resulting time series is:

   O1MAR1999    30
   O1APR1999    .
   O1MAY1999    20

If the ACCUMULATE=STDDEV option is specified, the resulting time series is:

   O1MAR1999    14.14
   O1APR1999    .
   O1MAY1999    17.32

As you can see from the preceding examples, the accumulated time series can have missing values even though the data set observations contain no missing values.

Boundary Alignment

When the BOUNDARYALIGN= option is used to qualify the START= or END= options, additional time series values can be incorporated into the accumulation operation. For example, suppose a data set contains the following observations:

   01JAN1999  10
   01FEB1999  10
   01MAR1999  10
   01APR1999  10
   01MAY1999  10
   01JUN1999  10

If the options START=01FEB1999d, END=01APR1999d, INTERVAL=QUARTER, and ACCUMULATE=TOTAL are specified, using the BOUNDARYALIGN= option results in the following accumlated time series:

If BOUNDARYALIGN=START is specified, the accumulated time series is:

   01JAN1999  30
   01APR1999  10

If BOUNDARYALIGN=END is specified, the accumulated time series is:

   01JAN1999  20
   01APR1999  30

If BOUNDARYALIGN=BOTH is specified, the accumulated time series is:

   01JAN1999  30
   01APR1999  30

If BOUNDARYALIGN=NONE is specified, the accumulated time series is:

   01JAN1999  20
   01APR1999  10