Definition: Adjustment of seasonal variations
Seasonal adjustment, or the adjustment of seasonal variations, aims, after adjusting for calendar effects, to take account of the impact of the known seasonal factors that have been observed in the past.
For example, in the case of the production index, annual summer holidays have a negative impact on industrial production. The level of this impact varies according to the country being studied and whether or not observation units close. It also depends on the area of activity concerned. In addition, the situation is complicated as these practices/habits/traditions change over time. Most series, with the notable exception of prices, are seasonally adjusted. If thenational statistical office providing the data does the seasonal adjustment, these series are used. If no seasonally adjusted series are supplied, Eurostat perform the seasonal adjustment.
Eurostat, "Quarterly Panorama of European business statistics", 1-2009, Office for Official Publications of the European Communities, Luxembourg, 2009