Use the Polynomial Specification window to add a polynomial to an ARIMA model. The set of lags defined here become a polynomial factor, denoted by a list of lags in parentheses, when you select “OK.” If you accessed this window from the AR Polynomial Specification window, then it is added to the autoregressive part of the model. If you accessed it from the MA Polynomial Specification window, it is added to the moving-average part of the model.