1. General aspects of the data validation process
ICP-Africa Regional Workshop
Pretoria, South Africa
June 2011

2. Outline General aspects of the data validation process
Introduction to data validation
General validation process
Validation stages

3. Why Data Validation?
These prices are used to calculate purchasing power parities (PPPs) which are further used to derive measures of price and
volume relatives
NCAs of the countries participating in the ICP provide the RCA with a set of purchasers’ prices
for a selection of items
The regional PPPs are then linked to form a global set of PPPs and measures of price and volume relatives
The measures are subsequently published by the RCA and the World Bank thereby reaching a variety of users including policy makers, economic analysts, researchers, politicians, journalists and the general public
It is therefore essential that the prices on which the PPPs are based on are rigorously checked and corrected i.e. validated

4. Objectives of the Data validation
1st objective Clean data from pricing errors
A price error occurs when a price or related metadata is recorded incorrectly or error is introduced afterwards in the process
A product error occurs when price collectors price products that do not match the product specification
2nd objective Ensure the comparability of prices
The aim of the comparison is to compare like with like; loose product specifications or difficult survey areas may introduce product errors
Cannot be attributed to the data of any particular country as they are not errors per se at the national level, given that the data is coherent at sub-national level

5. Process of the Data Validation
Validation stages
Intra-country
For regional items (incl. CGL)
National validation
NCAs
Inter-country
Regional validation
NCAs, RCAs
Inter-country across regions
For GCL items and regional PPPs
Global validation
NCAs, RCAs, GO

6. 1 2 Interaction during the Data Validation Validation Queries on
Quarterly Prices and Metadata
Annual Prices and Metadata
Validation Tables
PPPs by the ICP Classification
Quarterly Prices and Metadata
Annual Prices and Metadata 1 2
National Level
Regional Level
Global Level
Original or Edited
Original or Edited
Quarterly Prices and Metadata
Annual Prices and Metadata
Quarterly Prices and Metadata
Annual Prices and Metadata
Validation Tables
PPPs by the ICP Classification

7. Introduction to Country level validation
Intra-country validation is a stage carried out by the NCAs to establish that 1
Reported prices are correct 2
Price collectors within a country have priced products that match the product specifications 3
Survey frame worked as anticipated
Validation stage for items on regional item lists
Quarterly Data
National and sub-national
Annual Data

8. Introduction to Regional level validation
Inter-country validation is a stage carried out by the NCAs and RCAs to establish that 1
Countries within the region have correct i.e. error free data 2
Countries within the region have priced comparable products
Validation stage for items on regional item list
Quarterly Data
National and sub-national
Annual Data

9. Introduction to Global level validation
Global validation is a stage carried out by the NCAs, RCAs and the Global Office to establish that 1
Reported prices are correct 2
Price data between the regions is comparable 3
Global results are plausible
Validation stage for Global Core List items and Regional PPPs
Quarterly Data
National averages
Annual Data

10. Iterativeness during inter-country and global validation
Inter-country and global validation are iterative stages - cycle continues until the data is considered to be final
RCAs or the GO leading the process
NCAs to be pro-active
Different speeds within the region may need to be followed
Normally 4 rounds is sufficient for inter-country
Different speeds, overlapping price collection and validation needs careful planning
Original or edited price data and metadata sent to RCAs by NCAs
Validation tables or comparisons calculated by RCAs
Tables and comparisons delivered to all parties
Tables and comparisons analyzed by all parties
Data edited based on the findings

11. THANK YOU