Southern DA, McLaren L, Hawe P, Knudtson ML, Ghali, WA, for the APPROACH Investigators. Individual-Level and Neighborhood-Level Income Measures: Agreement and Association With Outcomes in a Cardiac Disease Cohort. Med Care 2005 Nov; 43:1116–1122.
Background: Census-based measures of income often are used as proxies for individual-level income. Yet, the validity of such area-based measures relative to ‘true’ individual-level income has not been fully characterized. Objectives: The objectives of this study were (1) to determine whether area-based measures of household income area suitable proxy for self-reported household income and (2) to assess whether these measures are associated with outcomes in a cardiac disease cohort.
Research Design: We used a prospective cohort from the Alberta Provincial Project for Outcome Assessment in Coronary Heart Disease (APPROACH©) cardiac catheterization registry.
Subjects: A total of 4,372 patients having undergone cardiac catheterization and who also completed a 1-year follow-up questionnaire on self-reported income level were studied.
Measures: Our measurements were survival to 2.5 years after catheterization and health-related quality of life (EuroQoL).
Results: Agreement between the 2 income measures generally was poor (unweighted Kappa =0.07), particularly for the low-income patients. Despite this poor agreement, both income measures were positively associated with survival and EuroQoL scores. An outcome analysis that simultaneously considered individual-level income and area-based income revealed that low-income individuals have poorer survival and lower quality of life scores if they live in low income neighborhoods, but not if they live in high income neighborhoods.
Conclusions: The area-based estimates of household income in these data demonstrate poor agreement with self-reported household income at the level of individual patients, particularly for low-income patients. Despite this, both income measures appear to be prognostically relevant, perhaps because individual and neighborhood income measure different constructs.