Frequently Asked Questions

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What indicates a good quality seasonal adjustment?

No residual seasonal effect. Once we adjust the series for seasonality, there should be no remaining seasonal effect in the adjusted series. The seasonally adjusted series is the combination of the trend-cycle and the irregular. Neither of these components should contain seasonality.

Passing values for quality assessment diagnostics. We look for M7 and Q statistics less than 1.0. These diagnostics help us decide if X-12-ARIMA can adequately adjust the series. Stability (small revisions) of the estimates X-12-ARIMA contains several different stability diagnostics to help us select X-12-ARIMA options to keep revisions of the estimates low. Besides selecting the best X-12-ARIMA options, we can also reduce revisions by running X-12-ARIMA every month to get concurrent seasonal factors and by using ARIMA forecasts that make it possible to use symmetrical averaging formulas in the calculation of the seasonal factors, trend-cycle, and irregulars.

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