General aspects of the data validation process ICP-Africa Regional Workshop Pretoria, South Africa 20 - 24 June 2011

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

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

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

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

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

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

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

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

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

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