The X12 Procedure

ADJUST Statement

ADJUST option ;

The ADJUST statement adjusts the series for leap year and length-of-period factors prior to estimating a regARIMA model. The Prior Adjustment Factors table is associated with the ADJUST statement.

The following option can appear in the ADJUST statement:


specifies length-of-month adjustment, length-of-quarter adjustment, or leap year adjustment. PREDEFINED=LOM and PREDEFINED=LOQ are equivalent because the actual adjustment is determined by the interval of the time series. Also, because leap year adjustment is a limited form of length-of-period adjustment, only one type of predefined adjustment can be specified. The PREDEFINED= option should not be used in conjunction with PREDEFINED=TD or PREDEFINED=TD1COEF in the REGRESSION statement or MODE=ADD or MODE=PSEUDOADD in the X11 statement. PREDEFINED=LPYEAR cannot be specified unless the series is log transformed.

If the series is to be transformed by using a Box-Cox or logistic transformation, the series is first adjusted according to the ADJUST statement, and then it is transformed.

In the case of a length-of-month adjustment for the series with observations $Y_ t$, each observation is first divided by the number of days in that month, $m_ t$, and then multiplied by the average length of month (30.4375), resulting in $(30.4375 \times Y_ t)/m_ t$. Length-of-quarter adjustments are performed in a similar manner, resulting in $(91.3125 \times Y_ t)/q_ t$, where $q_ t$ is the length in days of quarter $t$.

Forecasts of the transformed and adjusted data are transformed and adjusted back to the original scale for output.