Background People who acquire a disability experience large deterioration in their mental health, and the extent of the effect varies widely. Socioeconomic characteristics may modify the effect, however no single study has examined this comprehensively. This is an important omission as it may offer a better understanding of the mechanisms linking disability and poor mental health and elucidate vulnerable subgroups of the population of people with disabilities. The aim of this study was to identify key demographic and socioeconomic factors that modify the effect of disability acquisition on mental health, to identify characteristics that make people who acquire a disability vulnerable to poor mental health outcomes as a basis for targeted interventions.

Methods We used four waves of data from the Household, Income and Labour Dynamics in Australia Survey to characterise disability acquisition (2011–2014). The analysis was restricted to individuals who acquired a disability (reported two consecutive waves with no disability followed by two consecutive waves with disability; n = 294) and those who remained disability-free for all four waves (n = 5717). Mental health was measured in the final wave using the Mental Health subscale of the Standard Form 36 (SF-36) health questionnaire score (mean: 74.7; standard deviation: 18.1; range: 0 to 100). We used linear regression models, applying a propensity score method which uses inverse probability of treatment weighting to better control for confounding, to estimate the effect of disability acquisition on mental health. We tested for effect measure modification by a priori factors identified using a causal diagram that included key demographic and socioeconomic variables.

Results There was evidence that education, employment, income, wealth, housing tenure and having children modified the effect (p < 0.05), with larger negative effects of disability acquisition on mental health found for people who did not complete secondary education, were unemployed or not in the labour force, were in the poorest income quintile, had low wealth, people living in public rental housing, and those who had children. The greatest disparities between people who acquired a disability and those who did not were seen for income (lowest quintile: −14.7, 95% CI −22.4, −7.0 versus highest quintile: −3.4, 95% CI −9.0, 2.2) and housing tenure (public rental accommodation: −23.0, 95% CI −30.1, −15.9 versus mortgagors: −2.0, 95% CI −5.2, 1.2).

Conclusion People who acquire a disability who experience socioeconomic disadvantage prior to disability are particularly vulnerable to poor mental health outcomes.