A second consideration represents diverse domains, but the common theme is the importance of assessing alternative aspects of the individual. The risk here is essentially of ‘third-variable’ confounds, or potential relationships with alternative or unmeasured variables that lead to spurious conclusions. In other words, genetic variables or discounting variables may be associated with each other by virtue of a common association with an alternative characteristic, so it is important to thoroughly examine and incorporate variation on related domains to rule out false positives (or false negative). In particular, this applies to both collateral demographic and cognitive factors. As a decision-making phenotype, the typical delay discounting task using money as a commodity is necessarily contextualized within factors such as the individual’s socioeconomic status; as well as cognitive processing factors, such as working memory and attention. In the first case, income has typically not been found to be substantially related to discounting (e.g., MacKillop & Tidey, 2011), but this is not always the case and the role of income should be considered nonetheless. In contrast, aspects of cognitive function have been consistently
