Census II X-11 (Additive and Multiplicative)
Census X-11 is a refinement of the seasonal-decomposition method. It seasonally adjusts and decomposes your data through a series of predefined steps: seasonal, trend, cycle and random or irregular. A seasonal component of a time series occurs regularly (for example, Christmas; you know when it’s going to happen) while a cycle has a duration that varies from cycle to cycle (i.e. economic variables are cyclical. A depression occurs at irregular intervals). During the forecasting process, Census X-11 factors in trading days to refine the forecast and reduce the irregular component of the forecast by weighting each period by the number of trading days.