Understanding how a digital mental health intervention can be optimised to ensure effectiveness in the longer-term: findings from a causal mediation analyses of the CONEMO trials

BackgroundTwo CONEMO trials in Lima, Peru and Sao Paulo, Brazil evaluated a digital mental health intervention (DMHI) based on behavioural activation (BA) that demonstrated improvements in symptoms of depression between trial arms at three-months, but not at six-months. To understand how we can optimize CONEMO in the longer-term, we therefore aim to investigate mediators through which the DMHI improved symptoms of depression at six-months, separately for the two trials and then using a pooled dataset. MethodsWe used data that included adults with depression (Patient Health Questionnaire - 9 (PHQ-9) score [≥]10) and comorbid hypertension and/or diabetes. Interventional effects were used to decompose the total effect of DMHI on symptoms of depression at six months into indirect effects via: understanding the content of the sessions without difficulty; number of activities completed that were self-selected to improve levels of BA; and levels of activation measured using the Behavioural Activation for Depression Short Form (BADS-SF). FindingsUsing the pooled dataset, understanding the content of the sessions without difficulty mediated a 10% [0.10: 95% CI: 0.03 to 0.15] improvement in PHQ-9 scores at six months; completing self-selected activities mediated a 12% improvement [0.12: 0.01 to 0.23]; and, lastly, BA mediated a 2% [0.02: 0.01, 0.05] improvement. ConclusionsOur findings suggest that targeting participants to complete activities they find enjoyable will help to improve levels of activation and maintain the effect of the CONEMO intervention in the longer-term. Improving the content of the sessions to facilitate understanding can also help to maintain improvements.