摘要：Objectives . This study sought to determine whether income inequality, household income, and their interaction are associated with health status. Methods . Income inequality and area income measures were linked to data on household income and individual characteristics from the 1994 Canadian National Population Health Survey and to data on self-reported health status from the 1994, 1996, and 1998 survey waves. Results . Income inequality was not associated with health status. Low household income was consistently associated with poor health. The combination of low household income and residence in a metropolitan area with less income inequality was associated with poorer health status than was residence in an area with more income inequality. Conclusions . Household income, but not income inequality, appears to explain some of the differences in health status among Canadians. The idea that the distribution of income within a population (i.e., income inequality) could be an important determinant of health has spurred a large and growing research literature. 1 Recently, the relationship between income inequality and area-level measures of health status has been called into question. 2, 3 The early work that reported an inverse relationship between income inequality and life expectancy and a positive relationship between income inequality and mortality across industrialized countries 4– 7 has been reexamined and its conclusions shown to be a function of sample selection, time period, or data quality. 8– 10 Research that has examined the relationship between income inequality and area-level measures of health status within countries has generally shown a negative relationship. 11– 16 Exceptions include 1 study involving Canadian data 17 and 2 studies involving American data that controlled for area-level measures of educational attainment or racial concentration. 18, 19 Controlling for educational attainment and racial concentration may be inappropriate, however, because these area-level attributes could represent pathways through which income inequality affects health. 20 Ecological studies have been criticized on both theoretical and methodological grounds. 21, 22 Most important, the relationship between income inequality and area-level measures of health status can arise from a nonlinear and diminishing relationship between individuals’ income and their health status. 23– 25 Because area-level data alone cannot fully address this possibility, many researchers have turned to multilevel data. US studies involving the use of crosssectional designs and multilevel data have consistently revealed a relationship between income inequality and individuals’ health status in regard to a variety of health outcomes at the state or county level 26– 30 but not at the metropolitan level 30 ; studies conducted in Japan 31 and the United Kingdom 32 have not revealed such a relationship. Declines in health status may lead to declines in income, 33 however, and if such transitions are concentrated geographically, declines in health status could increase income inequality. Studies using cohort designs and multilevel data, which have the potential to account for such sequencing, have produced mixed results when they have examined the relationship between income inequality and individuals’ health status over time in the United States 34– 38 and have revealed no relationship in Denmark. 39 It may be premature, however, to reject the income inequality hypothesis. First, a number of possible reasons have been identified for the mixed results observed in the United States, such as sample selection, differences in income inequality and health measures, misspecification of individuals’ income, and confounder selection. 1, 3, 18 Second, to our knowledge, only 1 study involving the use of a cohort design and multilevel data has been conducted outside the United States. 39 Third, even if income inequality does not independently affect health, it may interact with individuals’ income. 40 This study extended previous research by examining whether income inequality at the metropolitan level, household income, or the interaction between income inequality and household income is associated with individuals’ health status over a 4-year period in Canada. We examined whether income inequality and average area income are associated with individuals’ health status after control for household income and other relevant confounders and potential pathways. In addition, we examined whether the relationship between income inequality and health status is different among low- and high-income individuals. We conceptualize income inequality as potentially affecting health status through neomaterialist mechanisms, psychosocial mechanisms, or both. 41, 42 The neomaterialist explanation hypothesizes that high levels of income inequality could negatively influence health through a systematic underinvestment in and inequity in access to other healthdetermining factors such as education, a clean environment, and health care. The psychosocial explanation hypothesizes that high levels of income inequality could lead to health-damaging reactions such as stress, anxiety, and shame in those who are worse off. An implication of the neomaterialist mechanism is that Canada’s universal health care system could lessen any relationship between income inequality and health status. The large and growing private health care market (e.g., for noninsured services such as prescription drugs) and regional and socioeconomic inequities in access to health care 43, 44 suggest that income inequality could still influence health status in Canada through differences among individuals in terms of access to health care.
