Urbanicity, posttraumatic stress disorder, and effect modification by socioeconomic position: A nested case-control study of the Korean National Health Insurance Database

We aimed to estimate the association between urbanicity and the onset of posttraumatic stress disorder (PTSD) and to investigate heterogeneity therein according to age and socioeconomic position (SEP).

We analyzed administrative data from the Korean National Health Insurance Database for patients with PTSD from 2004 to 2018 (N = 109,230) and for a 1:4 sample of age-, sex-, and enrollment year-matched controls. Information on eligibility, SEP (proxied by insurance premium), place of residence, diagnosis, and medical claims was obtained. Urbanicity of administrative districts was assessed using data from the Korean Statistical Information Service, 2005-2018. We estimated hazard ratios (HRs) from baseline and time-dependent models. Subgroup analyses and polynomial splines were used to investigate heterogeneity by age and SEP.

Urbanicity was associated with an increased risk of PTSD (per 10%p increase, HR = 1.056, 95% CI 1.050-1.061). A positive association was estimated among patients aged 0-29 years (HR = 1.115, CI 1.106-1.124), while negative associations were estimated among patients aged 30-64 years (HR = 0.990, CI 0.987-0.994) and 65 years or older (HR = 0.992, CI 0.979-1.014). The estimated associations with urbanicity were more prominent at the extremes of SEP, but only among younger participants.

Urban residence was associated with an increased risk of PTSD diagnosis. The estimated association was larger among younger individuals (but not among middle-aged and older individuals). Among younger individuals, the estimated association was larger at both extremes of SEP.