In addition to the binary diagnosis of AD, we chose to examine several quantitative alcohol-related traits because examining such traits provides more power than analysis of dichotomous phenotypes; prior research in this sample detected linkage and association signals with these traits (e.g., Kuo et al., 2006). We assessed age-at-onset of AD (ONSET), subjective response to ethanol, maximum drinks in 24 hours (MAX24), and a factor score of withdrawal symptoms (WDSFS). ONSET was defined as the age at which the first criterion for DSM-IV AD was satisfied. Subjective response to ethanol was assessed using the self-rating of the effects of ethanol (SRE, Schuckit et al., 1997) to form two scores, ISENS and tolerance/maximum drinking (TOLMX). The SRE inquires about how many drinks were needed for a subject to experience effects from alcohol consumption at different stages of use. ISENS is based on “the first 5 times you ever drank,” and items contributing to TOLMX concern the “period when you drank the most.” The score of each measure was computed by summing the number of drinks required to produce an effect and
