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. We observe a tightly estimated null effect even though the majority of subjects believed that planning is helpful and despite clear evidence that they engaged with the planning process.

Can financial incentives aid habit formation in people attempting to establish a positive health behavior? We provide evidence on this question from a randomized controlled trial of modest-sized incentives to attend the gym among new members of a fitness facility. Our experiment randomized 690 participants into a control group that received a $30 payment unconditionally or one of 3 incentive groups that received a payment for attending the gym at least 9 times over the first 6 weeks of membership. Two incentive treatment arms offered monetary payments of $30 and $60. The third incentive treatment, motivated by the endowment effect, offered a physical item worth $30. All three incentives had only small impacts on attendance during members' first 6 weeks and no effect on their post-incentive visit trajectories. We document substantial overconfidence among new members about their likely visits and discuss how overconfidence may undermine the effectiveness of incentive programs.