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

Background: Two 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 optimise 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.
Methods: We used data that included adults with depression (Patient Health Questionnaire vs 9 (PHQ9) score greater than or equal to 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).
Findings: Using 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 PHQ9 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.
Conclusions: Our 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.