Mediators of effects of a digital alcohol intervention for online help-seekers : Findings from an effectiveness trial

BACKGROUND: Digital alcohol interventions have been shown to exert effects in helping individuals reduce their drinking. However, little is known about the mechanisms which mediate such effects. The objective of this study was to estimate natural direct and indirect effects of a digital alcohol intervention. METHODS: This secondary analysis of mediated effects used data from a randomised controlled trial which included individuals with unhealthy alcohol use with access to a mobile phone aged 18 years or older in Sweden. The comparator was basic alcohol and health information. The digital intervention was centrally designed around weekly monitoring of consumption followed by feedback and tools to support behaviour change. Mediated effects were estimated using measures from 1-, 2-, and 4-months post-randomisation. Primary outcomes were total weekly consumption (TWC) and frequency of heavy episodic drinking (HED). A counterfactual framework was used to estimate three hypothesised mediators: importance, knowledge of how to change (know-how), and confidence. RESULTS: Between 25/04/2019 and 26/11/2020, 2129 participants were randomised. The intervention improved know-how and confidence, which in turn mediated the effects on TWC and HED at 2- and 4-months. Analyses with imputed data were not markedly different. CONCLUSIONS: A digital alcohol intervention was found to exert effects in reducing consumption by means of improving individuals' knowledge of how to reduce their consumption and confidence in their ability to reduce. The use of face-valid single item measures is a study limitation notwithstanding observed findings, as is attrition and lack of blinding of participants.