Brief Cutting Edge Report
The effect of pair-based monetary contingency contracts for weight loss: Results from a randomized controlled pilot study
Funding agencies: This research was funded by the School of Psychology at the University of Leeds as part of a funded PhD studentship.
Disclosure: The authors declare no conflict of interest.
Clinical trial registration: ISRCTN registry ID ISRCTN13972919.
Although pair-based contracts using pairs of friends/family members have been investigated by Zitter and Fremouw (Zitter RE, Fremouw WJ. Individual versus partner consequation for weight loss. Behav Ther 1978;9:808-813), this is theoretically unlikely to be effective, as no additional source of social support would be provided, and people are likely to be less motivated to avoid failure in front of a friend/family member than a stranger. Indeed, in the previous study by Zitter and Fremouw, anecdotal reports suggested that one partner within the friend/family member pairing often convinced the other to deviate from the weight loss regime.
Monetary contingency contracts (MCCs), in which deposited money is returned contingent on weight loss, could promote weight/adiposity reduction. This study piloted individual- and pair-based MCCs (when refunds are contingent on two individuals losing weight) and assessed effects on weight/body composition.
Seventy-seven participants with BMI greater than 25 kg/m2 were recruited. In a non-blinded, randomized controlled trial conducted in a university laboratory setting, participants were randomized in pairs via a computer-generated sequence to one of four conditions: partner with pair-based refund (P-PBR), partner with individual refund (P-IR), individual weight loss with individual refund (I-IR), or no MCC (comparison). Refunds were contingent on weight loss after 4 and 8 weeks; weight/body composition was measured at 0, 4, and 8 weeks. Primary outcome measures were change in weight and fat mass.
Seventy-seven participants (P-PBR n = 16; P-IR n = 20; I-IR n = 22; comparison n = 19) were recruited. Deposit amount was significantly positively associated with reductions in weight/BMI. At 8 weeks, the P-PBR condition reduced fat mass more than all other conditions (P < 0.05) and reduced weight/BMI more than the I-IR condition (P < 0.05).
The large effect of P-PBR on fat mass suggests it would be valuable to conduct a fully powered, randomized controlled trial of pair-based MCCs.