The Effect of Activities-based Subsidy on Body Fat Loss

This study, which spans 24 weeks (12 treatment, 12 post-treatment), aims to compare the effectiveness of 2 financial incentive structures - a conditional subsidy versus a goal reward - on fat loss. 600 overweight but otherwise healthy female Singaporeans or Permanent Residents will be recruited via 2 recruitment phases, 2 months apart from each other. Participants will be given an individual-tailored percentage body fat (PBF) goal and assigned to one of three interventions:

1. Subsidy treatment group (STG) - Participants will be awarded $X for reaching the PBF goal at the end of 12 weeks. Regardless of goal attainment, participants will also be reimbursed 50% of approved health-improving expenses up to a cap of $Y in the 12 weeks. The subsidy is voluntary and flexible, with no direct intervention from researchers - participants will submit receipts to the program website and simply be reimbursed at the end of the experiment. To prevent cheating, all receipts must bear the participants' full name or be justifiably traceable to them. When submitting the receipt to the program website, they must also specify the purpose of the expense - this serves as a psychological reminder to utilize the expense more meaningfully, while allowing us to discern better to approve or reject the reimbursement claim.
2. Cash treatment group (CTG). Participants will be awarded $(X+Y) for reaching the PBF goal at the end of 12 weeks.
3. Control. Other than the participation fees, no additional incentives will be provided.

All participants will be given an individual-tailored 12-week PBF goal. The formula for this goal will be set following the approval of the IRB, in consultation with medical and fitness professionals (including certified doctors and fitness trainers) to ensure that it is safe, challenging, and achievable. The base formula, which assumes a 5% weight loss as is often defined to be the medically significant level, is:

(P*W-x*5%*W)/(95%*W)

where P is PBF at baseline (week 1), W is body mass in kg at baseline, P×W is their body fat mass at baseline, and x, ranging between 0% and 100%, is the parameter that is set in consultation with professionals. At 100%, it implies that all 5% in weight loss is from fat, vice versa.