Towards a common revision for European statistics By Gian Luigi Mazzi and Rosa Ruggeri Cannata

1. Towards a common revision for European statisticsBy Gian Luigi Mazzi and Rosa Ruggeri Cannata Q2010 European Conference on Quality in Official Statistics 4-6 May 2010

2. Outline • Introduction • Background: definitions and classifications • Revisions practices for PEEIs European aggregates • Principles for a common revisions policy for European statistics • Issues related to common revisions policy at domain level • Conclusions Eurostat – Unit D5 Key indicators for European policies

3. Revisions • For the users: annoying phenomenon • For the producers: normal phenomenon to increase progressively quality and precision • Both: interested in gaining a better understanding of the revision process as well as in its analysis • Informed decisions based on • transparency of the production process • Clear and publically available dissemination strategy Eurostat – Unit D5 Key indicators for European policies

4. European Statistics code of Practice • Principle 8 Appropriate Statistical Procedures: revisions follow standard, well-established and transparent procedures • Principle 12 Accuracy and Reliability: studies and analyses of revisions are carried out routinely and used internally to inform statistical processes • Principle 15 Accessibility and Clarity: Statistics are presented in a form that facilitates proper interpretation and meaningful comparisons • PEEIS: EFC Status Reports on information requirements in EMU Eurostat – Unit D5 Key indicators for European policies

5. Background definitions of revisions • Definition 1: Any change in a value of a statistic released to the public by an official national or supranational statistical agency. When: • Definition 2: For a given time series we define vintage the set of data that was the latest release at a particular moment in time. • Definition 3: Historical data, catalogued and indexed by the date on which the data became available to the public, are referred to as “vintage” data (Anderson). • Alternative definition for revisions: Changes from an earlier vintage of estimates to a later vintage (Fixler and Grimm). Eurostat – Unit D5 Key indicators for European policies

6. Classifications of revisions • Revisions Classified by Reason • To incorporate better source data • To capture routine recalculation • To reflect improved methodology • To correct errors • Revisions Classified by Scheduling • Routine revisions • Annual revisions • Major revisions Eurostat – Unit D5 Key indicators for European policies

7. Effects of revisions • Revision of existing interpretations of the course of the indicator • Change of economic forecasts and policy implications • Qualification of user interpretations of current and recent observations • Information on the expected reliability of existing and future values • Qualification of the degree of confidence • Monitoring the quality of the data production process Improvement of the production process Eurostat – Unit D5 Key indicators for European policies

8. Revisions practices for PEEIsEuropean aggregates • HICP: follow Commission regulation • heterogeneous practices: • the number of times a figure could get revised is varying • the extent of revisions back in time too: routine revisions could cover just few values, values up to one year or the entire series • Trade-off: updated information towards less frequent revisions Eurostat – Unit D5 Key indicators for European policies

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11. Issues related to common revisions policy at domain level (1) • Routine revisions • Concurrent adjustment • Current adjustment • Mixing the two strategies • Choice based on: • Presence of a bias in the first data release • Randomness of the revisions process • Degree of volatility of the indicator Eurostat – Unit D5 Key indicators for European policies

12. Issues related to common revisions policy at domain level (2) • Threshold + Avoid unnecessary revisions + Reduce the number of revisions - Small but significant revisions could be discarded • Affects aggregation constraints Threshold Level should depend on the characteristics of the generating process Eurostat – Unit D5 Key indicators for European policies

13. Issues related to common revisions policy at domain level (3) • Extent back in time: largely varying, from few ones to the whole series • routine revisions should involve a limited number of periods • annual ones a larger number • Avoid inconsistencies over the time as well as breaks • Revise the whole series within a multi-annual benchmarking or rebasing exercise at regular intervals • Inform users on the extent of different kind of revisions Eurostat – Unit D5 Key indicators for European policies

14. Issues related to common revisions policy at domain level (4) • Infra-annual time series: revisions policy of seasonally adjusted data • Specific issues of the generating process to be considered at domain level • ESS guidelines on seasonal adjustment • Revisions of raw data • Concurrent adjustment, partial concurrent adjustment, Current adjustment, controlled current adjustment Eurostat – Unit D5 Key indicators for European policies

15. Revisions Analysis • OECD, member states, ECB vintage databases or data warehouses • PEEIs vintage database • Handbook on revisions analysis Eurostat – Unit D5 Key indicators for European policies

16. Conclusions • Lack of harmonisation in current existing revisions practices for Europeans statistics (in particular PEEIs) • Need for a general framework for a common revisions policy within the ESS • To be complemented by domain revisions policies • Will increase: • Transparency of the revision process • Data comparability • Harmonisation • Quality of European aggregates Eurostat – Unit D5 Key indicators for European policies

17. Thank you for your attention! Eurostat – Unit D5 Key indicators for European policies