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Seasonal adjustment

Seasonal Adjustment (SA) aims at estimating and removing seasonal and typical calendar effects from time series so that the seasonal and calendar fluctuations disappear from the series. A seasonally adjusted series is therefore a raw series from which the seasonality and the calendar effects have been removed.

SA is necessary to improve comparability over time (to compare for example the first quarter to the fourth quarter) and over space of time series (to compare for example European and national economies). High quality SA data play a crucial role in short term analysis and forecasting, policy and decision making.

Several activities are currently under development in order to achieve a higher degree of harmonization of the Eurostat and ESS practices on SA. They concern mainly:

  • Definition of detailed guidelines on SA      
  • Maintenance and development of reliable tools for SA (at ESS level) incorporating the most common procedures (Tramo Seats and X12Arima)
  • Fostering the exchange of practices among NSIs

  • Organisation of training on SA

ESS Guidelines on Seasonal Adjustment

ESS Guidelines on Seasonal Adjustment ESS Guidelines on Seasonal Adjustment

ESS Guidelines on Seasonal Adjustment have been endorsed by the Statistical Programme Committee on 14 February 2008 which supported their implementation by statistical domain and country.

This important achievement has been possible thanks to the intensive collaboration of Eurostat, the European Central Bank (ECB) and Member States through the Steering Group on seasonal adjustment. The guidelines have also benefit of the valuable contribution of international experts.

ESS guidelines represent an important step towards the harmonisation of seasonal and calendar adjustment practices within the ESS and in Eurostat. A common policy for the seasonal and calendar adjustment of Principal European Economic Indicators (PEEIs) and more generally of all infra-annual statistics will improve the quality and comparability of the national data as well as enhance the overall quality of European Union and euro area aggregates.

The guidelines cover all the key steps of the seasonal and calendar adjustment process. They are structured in seven main chapters:

Seasonal adjustment: benefits and costs

  • Pre-treatment of time-series
  • Seasonal adjustment
  • Revision policies
  • Quality of seasonal adjustment
  • Specific issues on SA
  • Data presentation issues

Each chapter, except for the first, is further subdivided into specific items. Each item presents:

  • the description of the issue
  • the list of options which could be followed to perform the concerned step
  • a prioritized list of three alternatives from the most recommended one to the one to be avoided
  • a synthetic list of main references.

The added value of such structure consists of the presentation of both the theoretical aspects and the practical implementation issues in a friendly and easy to read framework, useful as well as for experienced users and beginners.
Last update 10.11.2009