How planning facilitates behaviour change: Additive and interactive effects of a randomized controlled trial

Planning interventions have proven effective to change behaviour. However, less is known about their underlying mechanisms. To better understand the processes by which planning interventions unfold their effects, a combined action planning and coping planning intervention was tested in a field setting, with the focus on mediating and moderating effects of theory-derived social-cognitive variables. In a randomized controlled trial, 374 employees of a logistics company were asked to participate in either a combined action planning and coping planning intervention or an active control group. Four weeks later, self-reported changes in fruit and vegetable intake, action planning, coping planning, intentions and self-efficacy were measured. Single and simultaneous mediating effects on behaviour were tested with intention-to-treat analyses, along with interaction effects between planning processes. Action planning and coping planning mediated intervention effects on fruit and vegetable intake not only separately, but also simultaneously (multiple mediation). Action planning and coping planning had main and interactive effects on behaviour change (moderation). Action planning and coping planning may exert both additive and synergistic effects on health behaviour change. Volitional interventions should include both action planning and coping planning components and stimulate the use of planning in everyday life. Copyright (C) 2009 John Wiley & Sons, Ltd.