Data Requirements
You should have ample data for the series that you forecast
using PROC FORECAST.
However, the results may be poor unless you have a good deal more
than the minimum amount of data the procedure allows.
The minimum number of observations required for the different methods
is as follows:
- If METHOD=STEPAR is used, the minimum number of nonmissing
observations required for each series forecast is the TREND= option
value plus the value of the NLAGS= option.
For example, using NLAGS=13 and TREND=2,
at least 15 nonmissing observations are needed.
- If METHOD=EXPO is used, the minimum is the TREND= option value.
- If METHOD=WINTERS or ADDWINTERS is used, the minimum number of
observations is either the number of observations in a complete seasonal
cycle or the TREND= option value, whichever is greater.
(However, there should be data for several complete
seasonal cycles, or the seasonal factor estimates may be poor.)
For example, for the seasonal specifications SEASONS=MONTH,
SEASONS=(QTR DAY), or SEASONS=(MONTH DAY HOUR),
the longest cycle length is one year,
so at least one year of data is required.
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
