Although the notion of delay discounting as an addiction endophenotype is relatively recent, there is nonetheless accumulating support from a number of domains. As discussed previously, there is converging evidence that discounting is robustly associated with addictive behavior. In addition, there is evidence that it meets the core endophenotype criteria. To start with, a number of studies have found discounting preferences to be relatively stable over time. Robust reliability has been demonstrated in adolescents and adults over numerous time intervals, including one week (Baker, Johnson, & Bickel, 2003; Clare, Helps, & Sonuga-Barke, 2010; Simpson & Vuchinich, 2000), six weeks (Beck & Triplett, 2009), two months (Takahashi, Furukawa, Miyakawa, Maesato, & Higuchi, 2007), three months (Takahashi et al., 2007; Weatherly, Derenne, & Terrell, 2011), one year (Kirby, 2009), and even multiple years (Anokhin et al., 2011; Audrain-McGovern et al., 2009).
