Transcript UNECE Workshop on Seasonal Adjustment 20 – 23 February 2012, Ankara, Turkey Internal documentation and user documentation Anu Peltola Economic Statistics Section, UNECE.

UNECE Workshop on Seasonal Adjustment
20 – 23 February 2012, Ankara, Turkey
Internal documentation and
user documentation
Anu Peltola
Economic Statistics Section, UNECE
Overview
Main types of documentation
 Internal documentation
 User documentation
 Releasing metadata
 Communicate quality issues
 Assess and explain revisions
 Clear presentation

February 2012
UNECE Statistical Division
Slide 2
Main Types of Documentation

Metadata for users
•
Varying information needs
Documents needed for production
 The resulting data itself

•
At least raw data and seasonally adjusted
data to be stored as data vintages
• Good for revision analysis
February 2012
UNECE Statistical Division
Slide 3
Internal Documentation
Internal documentation comprises the following:
Step-by-step working instructions for
performing seasonal adjustment
 Internal quality reports
 Regularly updated lists of national holidays
 Lists for monitoring and enumerating the
reasons for outliers

February 2012
UNECE Statistical Division
Slide 4
Demetra+
Presents a considerable amount of
quality diagnostics
 For the key series you may store the
results of adjustment at least when reidentifying the model

•

i.e. The summary statistics of the Results
panel
Invest more time on documenting the
key time series
February 2012
UNECE Statistical Division
Slide 5
Some International Guidelines
The Fundamental Principles of Official Statistics
(UNECE, 1992)
 The Guidelines for the Modelling of Statistical
Data and Metadata (UNECE, 1995)
 The ESS Guidelines on Seasonal Adjustment

February 2012
UNECE Statistical Division
Slide 6
Design User Documentation Well

Due to excess of information
•
•

Give only relevant information
Direct the user to more detail (link)
Put emphasis on:
1. Understanding the idea of seasonal adjustment
2. Knowing how to use the data
3. For specialists information for replicating the results

You may use the metadata template of the ESS
Guidelines for defining the contents
February 2012
UNECE Statistical Division
Slide 7
1. General Explanation
Offer metadata for understanding statistics:
“Seasonal adjustment is the process of estimating and
then removing from a time series influences that are
systematic and calendar related. Observed data need to
be seasonally adjusted, as seasonal effects can conceal
both the true underlying movement in the series as well as
certain non-seasonal characteristics which may be of
interest to analysts.”
- By the Australian Bureau of Statistics
February 2012
UNECE Statistical Division
Slide 8
2. How to Use Data?
For example, explain reading indices to users:



The name “index” comes from Latin and means a pointer
It allows for comparison in time and space.
A cup of coffee cost 3 Swiss francs in 2011, whereas it
was 2.4 francs in 2005
new observation
3.0

 100  125
observation of the base period
2.4

Here, the year 2005 is our base period. The index number
for 2005 is 100, and the comparable figure for 2011 is 125.
The result indicates a price increase of 25 per cent.
February 2012
UNECE Statistical Division
Slide 9
3. Metadata for Own Seasonal
Adjustment









Seasonal adjustment method
(e.g.TRAMO/SEATS or X-12-ARIMA)
Software (e.g. Demetra+)
General decision rules applied
Describe the quality of the raw data
Means for outlier detection and correction
Choices in calendar adjustment and national holidays
Set of core quality diagnostics
Timing and reasons for revisions
Contact information to experts
February 2012
UNECE Statistical Division
Slide 10
Practices for Dissemination of
Metadata - OECD
” All statistical agencies should:


Compile metadata required for users to
understand the strengths and limitations of
the statistics it describes; and
Keep their metadata up-to-date, incorporating
the latest changes in definitions, classifications
and methodology, etc. “
February 2012
UNECE Statistical Division
Slide 11
Metadata to Accompany
Each Release

Ensure an easy access to the metadata
•
Direct the reader to the more detailed information
with a link from releases, tables and graphs +
add to printed publications
• Lead to a quality report for the indicator
• You may offer an archive of historical revisions
• Metadata in native and some other languages,
such as English
February 2012
UNECE Statistical Division
Slide 12
Metadata to Accompany
Each Release – UK example

Extracted from the end of a news release:
http://www.ons.gov.uk/ons/dcp171778_241735.pdf
February 2012
UNECE Statistical Division
Slide 13
What to Say about Data Quality


In general, metadata for the statistical indicator will:
• Describe the quality of the raw data (length and
appropriateness for adjustment)
• Inform about any breaks in the series
• Explain the definitions being measured
• Limitations of use
• Compilation methods and weighting system
• Treatment of changes
• Departures from international standards
Provide at least a minimum amount of information to
enable assessment of reliability
February 2012
UNECE Statistical Division
Slide 14
Outliers to be Explained

Outliers stay visible in the adjusted data
•
•
•
•

They contain information about events
Understanding the causes of outliers helps interpret
the data
Inform the user about the criteria for identifying
outliers
You may publish a list of events that caused outliers
Explain the difficulty with outliers in the end of
the series - duration and type isn't known until
new observations accumulate
•
A permanent level change or just one single peak?
February 2012
UNECE Statistical Division
Slide 15
Why Seasonal Adjustment
is Revised?
Offer an explanation to users, for example:
“There are two reasons that we revise seasonal
factors: We revise factors when we revise the
unadjusted data to achieve a better fit to the revised
data.” and “…when future data become available, we
use them to obtain improved seasonal factor estimates
for the most recent years of the series. These revised
factors lead to revised seasonal adjustments of higher
quality.”
- by the United States Bureau of Economic Analysis
February 2012
UNECE Statistical Division
Slide 16
Assess Revisions
Before Publishing



Demetra+ includes a revision history test
Use it to assess the likely size of revisions
Look at revisions to changes (previous/corresponding month)
February 2012
UNECE Statistical Division
Slide 17
Recommended Metadata for
Indices - OECD







Precise definitions of the underlying concepts
Index calculation methods - Laspeyres,
Paasche, Fisher
Strategy for constructing indices - fixed base or
chain index
Weighting system used, revision practices
Aggregation practices
Re-basing practices - procedures for linking
Treatment of changes
February 2012
UNECE Statistical Division
Slide 18
Clear Presentation




Similar but different series should be given
different titles
The precise name of the classification used in
statistics clearly indicated
When a field of activity is only partially
covered it should be clearly indicated for
instance with an asterisk or a footnote
Addition: Data corrected after the release
could be clearly indicated with an asterisk
February 2012
UNECE Statistical Division
Slide 19