The Limits of Simple Implementation Intentions: Evidence from a Field Experiment on Making Plans to Exercise

Recent large-scale randomized experiments find that helping people form implementation intentions by asking when and where they plan to act increases one-time actions, such as vaccinations, preventative screenings and voting. We investigate the effect of a simple scalable planning intervention on a repeated behavior using a randomized design involving 877 subjects at a private gym. Subjects were randomized into i) a treatment group who selected the days and times they intended to attend the gym over the next two weeks or ii) a control group who instead recorded their days of exercise in the prior two weeks. In contrast to recent studies, we find that the planning intervention did not have a positive effect on behavior and observe a tightly estimated null effect. This lack of effect is despite the fact that the majority of subjects believe that planning is helpful and despite clear evidence that they engaged with the planning process.