Income-related health inequalities in Canada and the United States: a decomposition analysis

Abstract

Objectives: We examined income-related inequalities in self-reported health in the United States and Canada and the extent to which they are associated with individual-level risk factors and health care system characteristics.

Methods: We estimated income inequalities with concentration indexes and curves derived from comparable survey data from the 2002 to 2003 Joint Canada-US Survey of Health. Inequalities were then decomposed by regression and decomposition analysis to distinguish the contributions of various factors.

Results: The distribution of income accounted for close to half of income-related health inequalities in both the United States and Canada. Health care system factors (e.g., unmet needs and health insurance status) and risk factors (e.g., physical inactivity and obesity) contributed more to income-related health inequalities in the United States than to those in Canada.

Conclusions: Individual-level health risk factors and health care system characteristics have similar associations with health status in both countries, but they both are far more prevalent and much more concentrated among lower-income groups in the United States than in Canada.

FIGURE 1

Income-related health inequalities in the United States and Canada, shown as (a) a hypothetical Lorenz/concentration curve and Gini coefficient/concentration index and (b) the difference between the Lorenz/concentration curve and the line of equality: Joint Canada–US Survey of Health, 2002–2003. Note. The situation representing perfect equality, in which every person has the same health, is shown by the diagonal dotted line (line of equality). A health Lorenz curve represents the cumulative proportion of a population's health as a function of the cumulative proportion of the population, where the population is ranked from lowest to highest health. A Gini coefficient for health inequality measures the deviation from the line of equality; it ranges from 0 to 1 and is defined as twice the shaded area. Concentration indexes are calculated the same way as Gini coefficients but can range from −1 to 1, depending on whether the health (or ill health) variable is more concentrated among individuals with lower income (negative concentration index values) or higher income (positive concentration index values).

FIGURE 2

Contributions to income-related health status inequalities in the United States and Canada from (a) demographic characteristics, (b) socioeconomic status, (c) lifestyle risk factors, and (d) health care system factors: Joint Canada–US Survey of Health, 2002–2003.