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

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

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

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

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

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

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

End-point Problem Turnover in Advertising March 2011

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

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

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

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

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

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

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

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

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

Source:ONS March 2011

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

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