Considering delay discounting as a phenotype simply refers to its phenomenology and measurement. As a behavioral characteristic, delay discounting refers to an individual’s profile of intertemporal reward preferences, or their preferences with regard to the tension between smaller rewards available in the short-term, typically the present, compared versus larger rewards available at a future time point. This profile can be operationalized in a number of ways and for an array of commodities. In children, preferences for smaller immediate rewards at the cost of larger delayed rewards can be assessed using the famous ‘marshmallow test’ (e.g., Mischel, Ebbesen, & Zeiss, 1972), in which participants are offered one marshmallow (or another candy) immediately or two when the experimenter comes back at some later point. In adolescents and adults, discounting is typically assessed using tasks comprising dichotomous items that pit smaller immediate rewards against larger delayed rewards, both in the common currency of money. These tasks use permutations of rewards and delays that systematically vary the options and quantify the effects of delay on the value of the larger reward. By plotting the
