The STATESPACE Procedure

VAR Statement

VAR variable (difference, difference, …) … ;

The VAR statement specifies the variables in the input data set to model and forecast. The VAR statement also specifies differencing of the input variables. The VAR statement is required.

Differencing is specified by following the variable name with a list of difference periods separated by commas. See the section Stationarity and Differencing for more information about differencing of input variables.

The order in which variables are listed in the VAR statement controls the order in which variables are included in the state vector. Usually, potential inputs should be listed before potential outputs.

For example, assuming the input data are monthly, the following VAR statement specifies modeling and forecasting of the one period and seasonal second difference of X and Y:

   var x(1,12) y(1,12);

In this example, the vector time series analyzed is

\[  \mb {x}_{t} = \left[\begin{matrix}  (1-{B})(1-{B}^{12})X_{t} - {\overline x}   \\ (1-{B})(1-{B}^{12})Y_{t} - {\overline y}   \end{matrix}\right]  \]

where B represents the back shift operator and ${{\overline x}}$ and ${{\overline y}}$ represent the means of the differenced series. If the NOCENTER option is specified, the mean differences are not subtracted.