Fiscella K, Franks P. Poverty or income inequality as predictors of mortality: longitudinal cohort study. British Medical Journal 1997; 314: 1724-8

This study looked at individual household incomes asked in a questionnaire, in a non-representative sample of US counties in 1971-75 and follow up mortality rates 7 to 15 years later. Certain categories of people, including the people living in poverty areas, elderly, and women of child bearing age were oversampled (that is sampled at higher proportional rates), and then the results later adjusted for this situation. This represents the first survey published that uses individual data, rather than information averaged out over the population. While there was a relationship between income inequality when interviewed earlier and mortality at the follow-up, when statistical controls were made for household income, the relationship disappeared. This suggests that the relative affect of hierarchy within a county or community is less important than the absolute income in that small area. It is difficult to evaluate inequality almost thirty years ago, when the relative discrepancies in social hierarchy were less because media power and penetration was considerably less. As with all such surveys, especially with few areas looked at in the US, and the problems with oversampling, the results need to be interpreted with caution. However, the authors conclude that "whether public policy focuses primarily on elimination of poverty or reduction in income disparity, neither goal is likely to be achieved in the absence of the other."_ 

Abstract

OBJECTIVE: To determine the effect of inequality in income between communities independent of household income on individual all cause mortality in the United States. 

DESIGN: Longitudinal cohort study. 

SUBJECTS: A nationally representative sample of 14,407 people aged 25-74 years in the United States from the first national health and nutrition examination survey.

SETTING: Subjects were followed from initial interview in 1971-5 until 1987. Complete follow up information was available for 92.2% of the sample. 

MAIN OUTCOME MEASURES: Relation between both household income and income inequality in community of residence and individual all cause mortality at follow up was examined with Cox proportional hazards survival analysis. 

RESULTS: Community income inequality showed a significant association with subsequent community mortality, and with individual mortality after adjustment for age, sex, and mean income in the community of residence. After adjustment for individual household income, however, the association with mortality was lost. 

CONCLUSIONS: In this nationally representative American sample, family income, but not community income inequality, independently predicts mortality. Previously reported ecological associations between income inequality and mortality may reflect confounding between individual family income and mortality.

Please click here to read complete text of the article

Keywords

• community
• confounding
• ecological studies
• household income
• income
• income inequality
• life expectancy
• mortality
• psychosocial factors
• relative deprivation
• socioeconomic status