The Impact of Disability Onset and Duration on Depression in South Korea: A Difference-in-Differences Analysis

Background and Purpose: In Korea, the prevalence of depression among people with disabilities (PWD), who experience life changes and daily challenges after disability onset, is higher than in the general population. Previous correlational studies have examined the association between disability and depression. However, the impact or causal effect of disability onset and duration on depression has been understudied. To address these gaps, we employed Difference-in-Differences (DD) to examine the causal effects of disability onset and duration on self-reported depression. We hypothesized that PWD would report higher levels of depression compared to those without disabilities, and that PWD with longer durations of disability would report higher levels of depression than those with shorter durations based on the cumulative disadvantage theory.

Methods: We analyzed Waves 1 to 18 of the Korea Welfare Panel Study, including 190,935 Koreans aged 19 or older at baseline. The exposure group (n = 7,009) experienced disability onset during the study period and had a disability duration of up to 17 years. The comparison group (n = 183,927) included individuals who never reported disability. The causal effect from the DD model was obtained from an interaction between disability status (exposure vs. comparison) and period (pre- vs. post-onset). The period was defined by the actual age of disability onset for the exposure group and the median onset age of the exposed used as “onset” for the control group. Sensitivity analyses were performed with alternative reference ages. To examine the effect of the duration of disability, we categorized disability duration into five intervals: pre-onset, 1–5 (reference), 6–10, 11–15, and 16 years or more, and used these variables in place of period, interacting with disability status. Time-varying covariates included centered age, self-rated health, and the COVID-19.

Results: Individuals with disabilities showed a significant decrease in depression after the onset, with an overall decline of -1.06 (p < .001, d = -0.27) relative to the change observed in the comparison group. The model with the interaction indicated that, among PWD, those with a disability duration of 6–10 years reported significantly lower levels of depression compared to those with a duration of 1–5 years (b = -0.63, p = .001, d = -0.16).

Conclusions and Implications: Our findings did not align with the perspective that disability onset worsens depression or the cumulative disadvantage theory. A possible explanation might be the theory of posttraumatic growth, suggesting that the onset of disability may function as a turning point initiating psychological adaptation. Indeed, several studies in Korea have reported that PWD with longer duration report higher levels of disability acceptance. That is, it could be that the longer the disability duration, the greater the psychological adaptation. These findings highlight the complex mental health trajectories among PWD and the need for tailored support based on disability-related contexts. Early after disability onset, interventions should focus on psychological changes resulting from onset and promote psychological growth; in the later stage, accumulated resources and experience could be leveraged to address long-term disability-related challenges and depression.