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Misclassification of Income Quintiles Derived from Area-based Measures

A Comparison of Enumeration Area and Forward Sortation Area

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Abstract

Background: Census-based methods are often used to estimate socioeconomic status. We assessed the agreement between Forward Sortation Area (FSA) and Enumeration Area (EA) derived income levels for all patients undergoing cardiac catheterization in Alberta, Canada, from 1995–1998.

Methods: Income quintiles were calculated from census data for FSA and EA level. FSAand EA-derived income measures were compared for misclassification. Both methods were then applied to the data to determine 4-year survival by income grouping in 21,446 patients following catheterization.

Results: The variability in EA-derived incomes for any given FSA-derived income is large. Only 40% of income quintiles are in agreement between the methods. For EA-based analyses, there is a linear relationship between higher income and lower mortality across all quintiles, while for FSA-based analyses, only the lowest income quintile had significantly higher mortality.

Discussion: Assuming that FSA-based methods are more likely to misclassify income compared to EA-based measures, the results for the FSA-based analyses are more likely to be erroneous. EA-derived measures should therefore be used when individual data are not available.

Résumé

Contexte: Les méthodes fondées sur le recensement sont souvent utilisées pour l’estimation du statut socio-économique. Nous avons examiné la concordance entre les revenus dérivés des régions de tri d’acheminement (RTA) et ceux dérivés des secteurs de dénombrement (SD) chez tous les patients ayant bénéficié d’un cathétérisme cardiaque en Alberta entre 1995 et 1998.

Méthodes: Nous avons comparé les mesures du revenu dérivées des RTA et des SD pour cerner d’éventuelles erreurs de classement. Ensuite, nous avons appliqué les deux méthodes aux données de 21 446 patients post-cathétérisme cardiaque afin de déterminer leur survie sur quatre ans.

Résultats: Pour toute valeur donnée des revenus dérivés des RTA, la variabilité des revenus dérivés des SD était grande, les revenus ne concordant d’une méthode à l’autre que dans 40% des cas. Ceci a des conséquences majeures dans l’analyse de l’association entre la survie et les quintiles de revenus: l’estimation de survie du quintile de revenus moyen selon les deux méthodes présente des différences significatives.

Interprétation: Les méthodes dérivées des RTA classifient mal les mesures du revenu et mènent à des résultats incorrects dans l’analyse de survie. Pour cette raison, nous proposons d’utiliser les mesures dérivées des SD si les données individuelles ne sont pas disponibles.

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Authors and Affiliations

  1. Department of Community Health Sciences, University of Calgary, HSG239, 3330 Hospital Dr. NW, Calgary, AB, T2N 4N1, Canada

    Danielle A. Southern MSc,  William A. Ghali MD, MPH & Peter D. Faris PhD

  2. Centre for Health and Policy Studies, University of Calgary, Canada

    Danielle A. Southern MSc, P. Diane Galbraith BN,  William A. Ghali MD, MPH, Peter D. Faris PhD & Merril L. Knudtson MD

  3. Department of Medicine, University of Calgary, Canada

    P. Diane Galbraith BN &  William A. Ghali MD, MPH

  4. Department of Public Health Sciences, University of Alberta, Edmonton, AB, Canada

    Colleen M. Norris PhD

  5. Department of Medicine, University of Alberta, Canada

    Michelle M. Graham MD

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  1. Danielle A. Southern MSc
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  2. P. Diane Galbraith BN
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  3. William A. Ghali MD, MPH
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  6. Merril L. Knudtson MD
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Correspondence to William A. Ghali MD, MPH.

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Southern, D.A., Galbraith, P.D., Ghali, W.A. et al. Misclassification of Income Quintiles Derived from Area-based Measures. Can J Public Health 93, 465–469 (2002). https://doi.org/10.1007/BF03405041

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  • DOI: https://doi.org/10.1007/BF03405041

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