Income inequality among American states and the conditional risk of post-traumatic stress disorder.

Purpose: Vulnerability to post-traumatic disorder (PTSD) following a traumatic event can be influenced by individual-level as well as contextual factors. Characteristics of the social and economic environment might increase the odds for PTSD after traumatic events occur. One example that has been identified as a potential environmental determinant is income inequality. The purpose of this study is to investigate the association between State-level income inequality and PTSD among adults who have been exposed to trauma.

Methods: We used data from the National Epidemiologic Survey on Alcohol and Related Conditions (n = 34,653). Structured diagnostic interviews were administered at baseline (2001-2002) and follow-up (2004-2005). Weighted multi-level logistic regression was used to determine if US State-level income inequality, as measured by the Gini coefficient, was associated with incident episodes of PTSD during the study's 3-year follow-up period adjusting for individual and state-level covariates.

Results: The mean Gini coefficient across states in the NESARC was 0.44 (SD = 0.02) and ranged from 0.39 to 0.53. Of the respondents, 27,638 reported exposure to a traumatic event. Of this sample, 6.9 and 2.3% experienced persistent or recurrent and incident PTSD, respectively. State-level inequality was not associated with increased odds for persistent or recurrent PTSD (OR = 1.02; 95% CI 0.85, 1.22), but was associated with incident PTSD (OR = 1.30, 95% CI 1.04, 1.63).

Conclusion: The degree of income inequality in one's state of residence is associated with vulnerability to PTSD among individuals exposed to traumatic events. Additional work is needed to determine if this association is causal (or alternatively, is explained by other socio-contextual factors associated with income inequality), and if so, what anxiogenic mechanisms explain it.