A randomised controlled trial testing the efficacy of a volitional help sheet supplemented with an implementation intention-reinforcement intervention designed to reduce mobile phone use while driving

Volitional help sheets (VHSs) promote the formation of implementation intentions (IF-THEN plans) and have recently shown promise for reducing mobile phone use while driving. We tested whether an intervention, designed to reinforce the extent to which the IF (critical situation) and THEN (goal-directed response) components of implementation intentions are encoded to memory, could generate additional reductions in drivers’ use of mobile phones over and above a VHS. Participants (N = 436) were randomised to either a VHS condition, a VHS plus implementation intention reinforcement condition, or an active control condition. There were no post-intervention differences between the conditions in standard self-report measures of mobile phone usage while driving, goal intentions, theoretically derived motivational pre-cursors of goal intentions (attitudes, subjective norms and perceived behavioural control) or memory ability. However, in the VHS plus implementation intention reinforcement condition, exploratory analyses indicated that the accuracy with which the participants re-specified their implementation intentions was associated with greater reductions in mobile phone usage. The extent to which participants can accurately re-specify their implementation intentions might constitute a useful measure of intervention adherence, which dictates whether VHSs can generate behaviour-change (e.g., reductions in mobile phone use while driving). Future research is required to test the extent to which this adherence measure moderates the effectiveness of VHSs and identify measures that distinguish between adherers and non-adherers.