Updating the evidence on the effectiveness of the alcohol reduction app, Drink Less: using Bayes factors to analyse trial datasets supplemented with extended recruitment

Background: A factorial experiment evaluating the Drink Less app found no clear evidence for main effects of enhanced versus minimal versions of five components but some evidence for an interaction effect. Bayes factors (BFs) showed the data to be insensitive. This study examined the use of BFs to update the evidence with further recruitment. Methods: A between-subject factorial experiment evaluated the main and two-way interaction effects of enhanced versus minimal version of five components of Drink Less. Participants were excessive drinkers, aged 18+, and living in the UK. After the required sample size was reached (n=672), additional data were collected for five months. Outcome measures were change in past week alcohol consumption and Alcohol Use Disorders Identification Test (AUDIT) score at one-month follow-up, amongst responders only (those who completed the questionnaire). BFs (with a half-normal distribution) were calculated (BF<0.33 indicate evidence for null hypothesis; 0.33<BF<3 indicate data are insensitive). Results: Of the sample of 2586, 342 (13.2%) responded to follow-up. Data were mainly insensitive but tended to support there being no large main effects of the enhanced version of individual components on consumption (0.22<BF<0.83) or AUDIT score (0.14<BF<0.98). Data no longer supported there being two-way interaction effects (0.31<BF<1.99). In an additional exploratory analysis, participants receiving four of the components averaged a numerically greater reduction in consumption than those not receiving any (21.6 versus 12.1 units), but the data were insensitive (BF=1.42). Conclusions: Data from extended recruitment in a factorial experiment evaluating components of Drink Less remained insensitive but tended towards individual and pairs of components not having a large effect. In an exploratory analysis, there was weak, anecdotal evidence for a synergistic effect of four components. In the event of uncertain results, calculating BFs can be used to update the strength of evidence of a dataset supplemented with extended recruitment.