A low level of response (LR) to alcohol is one of several endophenotypes related to a higher risk for the alcohol use disorders (AUDs) of abuse and dependence (Schuckit, 2009). A low LR is indicated by either a low intensity of reaction to alcohol at a given blood alcohol concentration (BAC) on an alcohol challenge (Schuckit and Gold, 1988; Schuckit & Smith, 2000), or as a retrospective report of the need for more drinks for effects earlier in life (Schuckit et al., 1997a, 1997b). This lower intensity of response relates to heavier alcohol intake even among relatively light and infrequent drinkers as young as age 12 (Schuckit et al., 2008a; 2008b). In all studies to date, a lower LR earlier in life predicted later heavier drinking and alcohol problems even after controlling for alcohol intake and pattern of problems at the time the response to alcohol was measured (Schuckit, 2009; Schuckit et al., 2008a; 2008b; Schuckit et al., in press; Volavka et al., 1996). The ability to control for baseline quantity is an important step to minimize the possibility that
