Socioeconomic inequality in the outcomes of a psychological intervention for depression for South Africans with a co-occurring chronic disease: A decomposition analysis

Task-shared psychological interventions are effective for reducing the severity of depression symptoms, but differences in treatment outcome by socioeconomic status is uncertain. This study examines socioeconomic inequalities (SEI) in depression outcomes among people with HIV and/or diabetes who participated in a cluster randomised controlled trial in the Western Cape Province of South Africa. The trial took place at 24 primary care clinics randomised to deliver a task-shared psychological intervention or treatment as usual (TAU). The trial enrolled 1119 participants meeting criteria for probable depression. Depression symptom severity was evaluated at baseline and 24-month follow-up. Using a concentration index (CI), SEIs in depression were assessed for the intervention and TAU arms. Demographic and socioeconomic variables were used to decompose the CI to identify contributors to SEI. Results indicate poorer participants at the intervention arm have significantly worse 24-month outcomes than wealthier counterparts (CI = - 0.080; SE = 0.025). Race (34.2%), unemployment (17.4%) and food insecurity (15%) were the main contributing factors. While policymakers need to invest in psychological interventions to reduce the burden caused by depression, this study suggests treatment outcomes may be different across the socioeconomic spectrum. Decomposition of these findings points to structural constraints, such as unemployment, as the key contributors towards poorer treatment outcomes. These findings suggest a need to combine psychological interventions with structural interventions that address the broader socio-economic determinants of mental health.