Income inequality among American states and the incidence of major depression.
BACKGROUND
Although cross-sectional and ecological studies have shown that higher area-level income inequality is related to increased risk for depression, few longitudinal studies have been conducted. This investigation examines the relationship between state-level income inequality and major depression among adults participating in a population-based, representative longitudinal study.


METHODS
We used data from the National Epidemiologic Survey on Alcohol and Related Conditions (n=34 653). Respondents completed structured diagnostic interviews at baseline (2001-2002) and follow-up (2004-2005). Weighted multilevel modelling was used to determine if U.S. state-level income inequality (measured by the Gini coefficient) was a significant predictor of depression at baseline and at follow-up, while controlling for individual-level and state-level covariates. We also repeated the longitudinal analyses, excluding those who had a history of depression or at baseline, in order to test whether income inequality was related to incident depression.


RESULTS
State-level inequality was associated with increased incidence of depression among women but not men. In comparison to women residing in states belonging to the lowest quintile of income inequality, women were at increased risk for depression in the second (OR=1.18, 95% CI 0.86 to 1.62), third (OR=1.22, 95% CI 0.91 to 1.62), fourth (OR=1.37, 95% CI 1.03 to 1.82) and fifth (OR=1.50, 95% CI 1.14 to 1.96) quintiles at follow-up (p<0.05 for the linear trend).


CONCLUSIONS
Living in a state with higher income inequality increases the risk for the development of depression among women.
Department of Social and Behavioral Sciences, Harvard School of Public Health, , Boston, Massachusetts, USA.
Roman
R
Pabayo
Ichiro
I
Kawachi
Stephen E
SE
Gilman
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D003865:Major Depressive Disorder / Q000453:epidemiology*; D004787:Environmental Pollution / Q000009:adverse effects; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D007182:Income / Q000706:statistics & numerical data*; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D055361:Multilevel Analysis; D011159:Population Surveillance; D012307:Risk Factors; D064890:Social Determinants of Health; D012959:Socioeconomic Factors; D014481:United States / Q000453:epidemiology; D055815:Young Adult
Cohort studies; Depression; Epidemiology; Inequalities; Mental Health