Abstract
Area-based markers of deprivation (e.g., postal codes) are commonly used to identify groups of people with low socioeconomic status (SES); the validity of this approach, however, remains unknown. In this study, we determined the accuracy of using income quintile groups calculated on the basis of the median family income of each forward sortation area (1996 Canadian census) to identify those living in poverty (i.e., annual family income of < $12,620). The sensitivity and specificity of using the lowest income quintile to capture those in poverty were 26% and 83%, respectively (likelihood ratio (LR) of 1.49; 99% CI, 1.49 to 1.50). Among those in non-metropolitan and metropolitan areas, the LRs were 1.26 (99% CI, 1.26 to 1.27) and 2.01 (99% CI, 2.01 to 2.02), respectively. The use of postal codes as the only marker to identify people with low SES may result in substantial misclassification of personal poverty, particularly in nonmetropolitan areas.
Résumé
On utilise communément les indicateurs de dénuement fondés sur la zone (p. ex., le code postal) pour définir les groupes de gens dont le statut socio-économique (SSE) est faible, mais on ignore encore la validité d’une telle approche. Dans notre étude, nous avons déterminé le degré d’exactitude de l’emploi de quintiles de revenus calculés selon le revenu familial médian dans chaque région de tri d’acheminement (Recensement canadien de 1996) pour identifier les personnes vivant sous le seuil de pauvreté (revenu familial annuel <12 620 $). La sensibilité et la spécificité de l’emploi du quintile de revenus inférieur pour identifier ces personnes étaient de 26 % et de 83 %, respectivement (rapport des vraisemblances (RV) de 1,49; IC 99 %, 1,49 à 1,50). Pour la population à l’extérieur des régions urbaines et en zone métropolitaine, les RV étaient respectivement de 1,26 (IC 99 %, 1,26 à 1,27) et de 2,01 (IC 99 %, 2,01 à 2,02). L’emploi du code postal comme seul indicateur des gens à faible SSE pourrait donc entraîner d’importantes erreurs de classement de la pauvreté individuelle, surtout à l’extérieur des régions urbaines.
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