Self-control for monetary and dietary rewards

Unlike children, adolescents take control over what they eat and how they spend their money. To remain healthy, they have to exercise self-control – forego the immediate pleasure of high-calorie foods for the prospect of being healthy in the future. These eating habits, established early on in life, tend to stay with individuals later on in their lives, contributing to the obesity epidemic. In Australia, one in four children (25%) are overweight or obese and it is predicted to increate to one in three by 2025.

Adolescents make real and consequential decisions related to their general wellbeing. To remain healthy, they have to exercise self-control – forego immediate pleasure of tasty but high-calorie foods for the prospect of being healthy in the future. These decisions often have health and economic impact later and throughout adulthood. It is now clear that adolescents more often than adults make decisions that impair their health outcomes in many forms, including excessive calorie intake and unhealthy food choices. These eating habits established early on in life tend to stay with individuals later in their lives, contributing to the obesity epidemic.

In a research project, we examined how adolescents make their dietary and money decisions at different time points. According to one common definition of self-control, behaviours that are labelled self-controlled usually involve not just choosing delayed rewards but also persisting in this choice until the delayed reward arrives. In economics, researchers usually model problems of self-control through time inconsistent preferences, such that agents have a “present bias” towards current consumption. By asking adolescents’ decisions on food and money at different time points, we aimed at investigating whether teenagers would show present bias (lack of self-control).

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697 Chinese high-school students participated in a five-week, incentivised longitudinal experiment where we elicited individual preferences for three reward types: money, healthy food and unhealthy food. Subjects faced the same set of decisions, featuring the same reward amounts delivered on the same dates, at two points in time. In the first session, all choices involved rewards to be received at two dates in the future, while in the second session the sooner rewards were available now.

We highlight several key findings. Fristly, at the median, averaging over all trials, our subjects choose to receive 2% more food on the sooner payment date when the decision is made on that day than when it is made in advance. This implies that, compared to a participant with self-control, our representative adolescent would consume around 246 more calories each week from the experiment alone, resulting in 1.6 kilograms increase in weight per year. Holding all else constant, an average high-school student with 𝐵𝑀𝐼 = 21 would become overweight in just 4 years. We also find strong present bias for money. At the median, subjects choose to receive 4% more money on the sooner payment date when the decision is made on that day than when it is made in advance.

Second, at an individual level, we find significantly positive and moderate correlations between individual measures of present bias for all reward type pairs, as well as between individual measures of impatience. Together, these findings imply that conventional choices over money are moderately predictive of choices for food, which may serve a good signal when researchers intend to extrapolate from existing studies for money to other domains.

Finally, we find that our experimental measures of self-control for both monetary and dietary rewards are predictive of subjects’ field behaviours. Adolescents who make less patient choices for any reward type are more likely to drink alcohol and have lower grades. Moreover, those who are more present biased for money and healthy food are more likely to drink alcohol and have lower grades.

Author:

Dr Xueting Wang is a lecturer in economics in the School of Economics, Finance and Marketing, in RMITs College of Business and Law.

Dr. Stephen Cheung is a senior Lecturer in Economics in the school of Economics, The University of Sydney.

Prof. Agnieszka Tymula is a Professor in Economics in the School of Economics, The University of Sydney.

The research presented in this article has been based on a recently published paper in Experimental Economics. You can read the full article here (open access).

22 March 2022

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Self-control for monetary and dietary rewards