In the decade of the eighties, several economic and institutional events have affected the pattern of the time series components, consequently, new problems on the accuracy and usefulness of the seasonally adjusted data emerged. Among these events, notable ones are the deep recession of 1981-1982; the introduction of new government regulations that enable business stores to be open longer hours and/or Sunday, and the early arrival of Easter (1980, 1983, 1985, 1986 and 1988). To cope with these problems, a significant amount of research was carried out at the Time Series Research and Analysis Division, that led to new developments and their implementation in X11ARIMA/88.

The X11ARIMA/88, as the X11ARIMA developed by Dagum (1980, here described in Chapters II and III), performs three basic functions: (1) Forecasting; (2) Seasonal adjustment; and (3) Composition of original and seasonally adjusted data. The new developments concern the first two key functions.