The when and how of planning: Meta-analysis of the scope and components of implementation intentions in 642 tests

When and how should one plan? We estimated the scope (when) of implementation intentions by computing effect sizes for different outcomes, samples, and study characteristics, and tested the components (how) of implementation intentions by analysing the format, processes of formation, and contents of plans. Across 642 independent tests, forming implementation intentions proved effective for cognitive, affective, and behavioural outcomes (.27 ≤ d ≤ .66). Effect sizes were larger when plans had a contingent (if-then) format, participants were highly motivated to pursue the goal, and plans were rehearsed. We developed a new taxonomy of the cues (e.g., time-and-place, task juncture) and responses (e.g., cognitive procedures, ignore- or inner speech-responses) specified in implementation intentions and tested their efficacy in promoting outcomes. Our review underlines the utility of implementation intentions in helping people regulate their thoughts, feelings, and actions and offers a taxonomy of plan contents that could inspire further tests of implementation intentions.