1. Carsten Boldsen Hansen Economic Statistics Section, UNECE
UNECE Workshop on Short-Term Statistics (STS) and Seasonal Adjustment
14 – 17 March 2011, Astana, Kazakhstan
How to Release Seasonally Adjusted Data ? (Examples of release practices, metadata, maintenance)
Carsten Boldsen Hansen
Economic Statistics Section, UNECE

2. Overview Quality of SA Revision policy Release practices Metadata
How to get started?
March 2011

3. Quality of SA
Release SA data after you are convinced about the quality
Explain possible quality issues to users
Quality of original data, length of time-series
Presence of strange features, outliers and volatility
Use more time with key indicators
Release documentation of all relevant seasonal adjustment steps
March 2011

4. Timing of Revisions SA data usually revised due to
Corrections and accumulation of raw data
Better estimates for the seasonal pattern
Revisions are welcomed
They derive from improved information set
Forecasts are replaced with new observations in SA
In SA one new observation can revise the past
Trade off between precision in SA data and stability of seasonal adjustment pattern
Revision should be scheduled in a regular way
March 2011

5. Nature of SA Revisions Industrial Production Index, Original Series
Release 9/2008
Release 11/2008
Release 12/2008
Release 10/2008
Source: Statistics Finland
March 2011

6. Nature of SA Revisions Industrial Production Index, Seasonally Adjusted
Release 12/2008
Release 11/2008
Release 9/2008
Release 10/2008
Source: Statistics Finland
March 2011

7. Features of the Trend Series
End of the trend series may change direction
Problems with defining trends
How smooth should it be vs. identification of turning points?
Should it include economic ‘cycles’ or just long-term structural effects?
Trend can have different annual totals from the original data
Trend is a good visual tool
March 2011

8. End-point Problem Turnover in Advertising
March 2011

9. Releasing Time Series
A. Publish raw and some adjusted data, e.g. one of the following:
SA series, SA plus WDA series, Trend-cycle series
B. Include only raw data in press releases
Too limited approach!
C. Present only levels or values
March 2011

10. Recommended Release Practices
Publish rather index numbers than monetary values
or both
Month-on-month and change from the same month one year earlier are both useful
A reference period needs to be determined
Provide long an coherent time series
Present the main contributors to change
Present products / enterprise groups / industries that are primarily responsible for the monthly movement
Source: Index of Industrial Production (UN)
March 2011

11. Revision Policy Revisions are inevitable to the quality of data
Be informative about the reasons for revisions
Methodological, accumulation, errors, changes to classifications
Users should be reminded of the size of the likely revisions
Correct errors as soon as possible
Revision policy be formulated: regular timing
Revisions to be carried back in time to maintain consistent time series
Normal revisions: no explicit info & monthly release
Prior information of large scale revisions
Source: Common Revision Policy for STS (EC) & Index of industrial production (UN)
March 2011

12. Advance Release Calendars
Use of advance release calendars is recommended widely
Reduces the chances of external interference with the release of statistics
IMF requires the countries that subscribe to the SDDS (but not GDDS) to provide advance release information
Statistics to be released as soon as the data becomes available and has been processed
March 2011

13. Proposed Release Practice
Include both raw and SA data in the release, details on the web site
Time series (raw, SA, WDA, trend)
Avoid annualized or cumulative growth rates as the only indicator
Avoid presentation of trend data in press releases
Trend series are good in graphs!
Release several growth rates
“Period on period” growth to be computed on SA data!
Annual growth to be computed on non-adjusted data
March 2011

14. Effect of Moving Holidays
Output of the national economy grew in April
Seasonally adjusted output rose by 1.2 per cent in April from the month before.
Year-on-year the increase amounted to 8.1 per cent according to the original series.
April 2008 included three working days more than the comparison month of the previous year. Adjusted for working days, the year-on-year growth was 5.1 per cent.
March 2011

15. Comparison of Countries Change from Previous Period
Source: OECD statistical news release
March 2011

16. Detecting Turning Points Change from the Previous Period
Source: UNECE weekly
March 2011

17. Smoothening of Development What is the direction of development?
Source: NSO of Tajikistan
March 2011

18. Source:ONS
March 2011

19. Metadata for Different Users
1. Non-technical explanation of SA
2. Enough metadata for assessment of reliability
3. Metadata to enable repetition of SA:
Method and software used
Decision rules, aggregation policy
Outlier detection and correction methods
Revision policy
Description of working day adjustment
Contact information
A metadata template is annexed to ESS guidelines on seasonal adjustment!
Source: OECD data and metadata reporting and presentation handbook
March 2011

20. Suggestions for Starting with SA
Assess your and users’ needs
Define a clear SA policy, covering:
Method, software, reanalysis, outliers, revision etc.
Choose simple and reliable method and software
Allocate sufficient resources and time
Train staff
Inform users:
about major events affecting seasonal adjustment
easy access to all relevant metadata
Do not publish until confident with the results
March 2011