Talk to a young adult who is planning to skip college so they can get a job and start working today. Try to explain to them that they could eventually make a lot more money if they graduated from college in four years with a marketable degree. Quite often they will be unmoved because $100 today is simply worth more to them than $400 four years from now. Psychologists call this relative judgment of worth “delay discounting.”
Many of us think that delay discounting affects young people more than older adults, perhaps because greater maturity and wisdom enables older adults to more clearly see the benefits of waiting until our earning power has increased. There are actually several different theories to explain why delay discounting lessens as we age, but some of those theories predict that delay discounting isn’t linear with age but rather “U-shaped” where delay discounting decreases with age up to a point and then increases again as we continue to grow older. Such a U-shaped discounting effect may make sense to us if we consider that a delay of ten years, say, may loom larger to a seventy year old than to a thirty year old.
Lu and colleagues decided to test the predictions of various theories of delay discounting by performing a meta-analysis of 105 relevant research studies. They found that those theories that predict a U-shaped discounting effect were indeed correct, but that the reasons for the U-shape are more complicated than just how many years one has left.
Abstract
A long-running debate about the developmental trajectory of delay discounting has received growing attention since 1994. Relevant theories, ranging from developmental psychology and evolutionary biology to behavioral economics, yield contradictory predictions. Encompassing a wide age range from 6.7 to 83.1 years, we evaluated these theories based on meta-analyses of 178 effect sizes from 105 articles that examined age-dependent delay discounting, providing up-to-date the most comprehensive review of the topic. Delay discounting decreased with advancing age (Fisher’s z = −.059). However, meta-regression suggested that this linear trend masked a U-shaped function, as implied by some theoretical models. We developed a derivative-based method and recovered this nonlinear function based on 58 effects. Both the meta-regression based on all 178 effect sizes and the derivative-based method convergently demonstrated that delay discounting was the lowest for middle-aged people around 50, depending on the magnitude of the reward. The U-shaped function was steeper for people with shorter life expectancies; the turning point comes at a younger age for medium-to-large rewards, and delay discounting models explained heterogeneity across studies. We expanded the current theoretical frameworks by synthesizing the life history theory and the antagonistic pleiotropy hypothesis. Built upon the mortality–fertility trade-off model of Sozou and Seymour (2003), we postulated the role of parental investment in postponing the increase of delay discounting in late adulthood, suggesting a three-way mortality–fertility–parenting trade-off. Possible proximate mechanisms were also discussed. Overall, when allocating assets over temporal intervals, a higher delay discount rate accompanies a lower future reproductive opportunity.
Citation
Lu, J., Yao, J., Zhou, Z., & Wang, X. T. (X.). (2023). Age effects on delay discounting across the lifespan: A meta-analytical approach to theory comparison and model development. Psychological Bulletin, 149(7-8), 447–486.
Dr Martin Fracker 