To capture discounting of delayed rewards empirically, the DDT poses participants with repeated choices between a smaller reward received immediately and a greater reward received after some time delay (e.g., “Would you prefer to have $65 today or $100 in a month?”). Over the course of the task, the amounts of immediate rewards are successively modified, as is the duration of delay. The individual's responses to the entire array of choices are then used to empirically derive their discounting function (i.e., how steeply they discount delayed rewards relative to immediate rewards, commonly denoted k). The DDT was administered with hypothetical money via a custom computer program [84] which is fully described in Supplementary File S1. Model fits of how well subjects' discounting functions fit Mazur's [85] nonlinear equation used to derive k values are calculated as R2 values. Erratic subjects and those with R2 values below 0.30 were excluded from principal analyses [86]. The DDT k value was normalized with a logarithmic transformation, as is typical in delay discounting research.
