ABSTRACT
This entry defines seasonality. Seasonality is relevant to all time-variant data and may affect time-invariant data but cannot be corrected for in that case. Three methods are described for deseasonalizing data, classical decomposition, X-12/X-13, and differencing. Detailed procedures are provided for performing classical decomposition. Some difficulties with deseasonalization are briefly discussed. Three methods for including seasonality within statistical models are briefly described.
