Context: In a natural experiment in which some families received income supplements, prevalence of adolescent behavioral symptoms decreased significantly. These adolescents are now young adults.
Objective: To examine the effects of income supplements in adolescence and adulthood on the prevalence of adult psychiatric disorders.
Design: Quasi-experimental, longitudinal.
Population and setting: A representative sample of children aged 9, 11, or 13 years in 1993 (349 [25%] of whom are American Indian) were assessed for psychiatric and substance use disorders through age 21 years (1993-2006). Of the 1420 who participated in 1993, 1185 were interviewed as adults. From 1996, when a casino opened on the Indian reservation, every American Indian but no non-Indians received an annual income supplement that increased from $500 to around $9000.
Main outcome measures: Prevalence of adult psychiatric disorders and substance use disorders based on the Diagnostic and Statistical Manual of Mental Disorders in 3 age cohorts, adjusted for age, sex, length of time in the family home, and number of Indian parents.
Results: As adults, significantly fewer Indians than non-Indians had a psychiatric disorder (106 Indians [weighted 30.2%] vs 337 non-Indians [weighted 36.0%]; odds ratio [OR], 0.46; 95% confidence interval [CI], 0.30-0.72; P = .001), particularly alcohol and cannabis abuse, dependence, or both. The youngest age-cohort of Indian youth had the longest exposure to the family income. Interactions between race/ethnicity and age cohort were significant. Planned comparisons showed that fewer of the youngest Indian age-cohort had any psychiatric disorder (31.4%) than the Indian middle cohort (41.7%; OR, 0.43; 95% CI, 0.24-0.78; P = .005) or oldest cohort (41.3%; OR, 0.69; 95% CI, 0.51-0.94; P = .01) or the youngest non-Indian cohort (37.1%; OR, 0.66; 95% CI, 0.48-0.90; P = .008). Study hypotheses were not upheld for nicotine or other drugs, or emotional or behavioral disorders. The income supplement received in adulthood had no impact on adult psychopathology.
Conclusion: Lower prevalence of psychopathology in American Indian youth following a family income supplement, compared with the nonexposed, non-Indian population, persisted into adulthood.