The Temporal and Sectoral Aggregation of Seasonally Adjusted Time

Procedures for the optimal seasonal adjustment of economic time series and their aggregation are derived, given a criterion suitable for the adjustment of data used in political or journalistic contexts. It is shown that data should be adjusted jointly and then temporally or sectorally aggregated, as desired, a procedure that preserves linear aggregation identities. Examination of actual economic time series indicates, that the optimal seasonal adjustment and aggregation of data provide a substantial improvement in the quality of sectorally disaggregated,, adjusted data and considerably reduces the required subsequent revision of current adjusted series