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.
The objectives of this study were (1) to determine whether area-based measures of household income are a suitable proxy for self-reported household income and (2) to assess whether these measures are associated with outcomes in a cardiac disease cohort.
We used a prospective cohort from the Alberta Provincial Project for Outcome Assessment in Coronary Heart Disease (APPROACH©) cardiac catheterization registry.
A total of 4372 patients having undergone cardiac catheterization and who also completed a 1-year follow-up questionnaire on self-reported income level were studied.
Our measurements were survival to 2.5 years after catheterization and health-related quality of life (EuroQoL).
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.
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.
From the *Department of Community Health Sciences and †Department of Medicine and ‡Centre for Health and Policy Studies, University of Calgary, Calgary, Alberta, Canada.
Dr. McLaren is supported by Postdoctoral Fellowships from the Canadian Institutes of Health Research and the Alberta Heritage Foundation for Medical Research. Dr. Ghali is supported by a Government of Canada Research Chair in Health Services Research and by a Health Scholar Award from the Alberta Heritage Foundation for Medical Research, Edmonton, Alberta. Dr. Hawe is Markin Chair in Health and Society, University of Calgary, Canada and supported as a Senior Scholar, Alberta Heritage Foundation for Medical Research. Dr. Knudtson receives partial support from the Libin Trust Fund. APPROACH was initially funded with a grant from the W. Garfield Weston Foundation. The ongoing operation of this project has been made possible by operating grants from the Heart and Stroke Foundation of Alberta, Northwest Territories, and Nunavut, and the Canadian Institutes of Health Research. The initiative also has received contributions from Alberta Health and Wellness, Merck Frosst Canada Inc, Monsanto Canada Inc–Searle, Eli Lilly Canada Inc, Guidant Corporation, Boston Scientific Ltd, Hoffmann-La Roche Ltd, and Johnson & Johnson Inc–Cordis.
Presented in abstract form at the 2004 Annual meeting of the Society of General Internal Medicine, Chicago, Illinois, May 2004.
Reprints: Dr. William A. Ghali, HSG239, 3330 Hospital Dr. NW, Calgary, Alberta, Canada, T2N 4N1. E-mail: firstname.lastname@example.org.