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WHO practices in imputation and estimation

Conference on Data Quality for International Organizations

Rome, Italy, 7-8 July 2008-05-28

Carla AbouZahrCoordinator, Statistics, Monitoring and Analysis

World Health OrganizationGeneva

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Types of health statistics

• Unadjusted health statistics derived directly from primary data collection with no adjustments or corrections.

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Types of health statistics

• Unadjusted health statistics derived directly from primary data collection with no adjustments or corrections.

• Adjusted health statistics corrected to deal with known biases, use of indirect techniques.

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Types of health statistics

• Unadjusted health statistics derived directly from primary data collection with no adjustments or corrections.

• Adjusted health statistics corrected to deal with known biases, use of indirect techniques.

• Predicted health statistics based on a model relating the quantity of interest to covariates. – Forecasting: past relationships to predict future– Farcasting: missing primary data

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Source:Gareth JonesWHO/UNICEF database

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Source:Christopher MurrayInstitute for Health Metrics and Evaluation

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Sources of data for global mortality estimates (circa 2004)

Complete VR Incomplete VR

Survey/census no data

Child mortality: q5 Adult mortality: 45q15

Source: WHO

Indirect methods problematic for adult mortality

Birth histories, Indirect methods;

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WHO principles for imputation

• Standard four-step procedure for estimation – a high-quality accessible database; – an independent peer review group; – published methods of estimation; margins of uncertainty– internal WHO clearance by HSI

• Country consultation– iterative process between Member States, WHO

country and regional offices and headquarters– feedback on quality of data collection and reporting;

strengthening country capacity to reproduce, produce and use estimates.

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External advisory bodies

• Disease-specific M&E reference groups– Include agencies and academic experts– Address coordination issues– Develop "best estimates": <5, maternal mortality,

coverage of interventions

• Advisory Committee on Health Monitoring and Statistics (ACHMS)– Independent outside experts – Gives inputs to WHO on its work, including Global

Burden of Disease, World Health Statistics.– Advises DG on scientific and technical issues.

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Summary and conclusion

• WHO use of imputation:– Correction for definitional differences, application

of WHO standards, known biases– Production of regional aggregates– Generation of missing values for countries

• Recommendations for CCSA– General principles for imputation– Methods context and subject specific– Transparency and replicability– Country endorsement of methods not values