Of course, cross-sectional associations cannot alone demonstrate causality, but a number of lines of evidence suggest that impulsive discounting at least partially predates addictive behavior and plays an etiological role. For example, in a large sample of adolescents, Audrain-McGovern et al. (2009) examined discounting and smoking behavior over a six year period and found that discounting predicted smoking initiation, not the other way around. These findings are similar to a previous finding that discounting assessed in pre-schoolers was associated with adult drug use 20 years later (Ayduk, Mendoza-Denton, Mischel, Downey, Peake, & Rodriguez, 2000). In addition, two retrospective studies have found high discounting in adolescence has been found to be associated with an earlier onset of symptoms of alcohol use disorders (Dom, D'Haene, Hulstijn, & Sabbe, 2006; Kollins, 2003). Finally, studies using animal models of discounting have found that impulsive discounting predicts acquisition and escalation of drug self-administration in drug-naïve animals (Anker, Perry, Gliddon, & Carroll, 2009; Marusich & Bardo, 2009; Perry, Larson, German, Madden, & Carroll, 2005; Perry, Nelson, Anderson, Morgan, & Carroll, 2007), convincingly suggesting that impulsive delay
