DSM-IV-defined alcohol abuse and dependence symptoms, including ages at onset and recency of each symptom, were assessed for all individuals who had ever had a full drink of alcohol. A five-level ordinal variable was constructed based on number of abuse and dependence symptoms endorsed (0, 1, 2, 3 or 4 or more); this variable was used in the variance components analysis described below (symptom categories were combined for descriptive purposes in tables). Lifetime AUD was operationalized in accordance with the proposed DSM-5 definition of AUD as occurrence of at least two of the 11 AUD symptoms (APA, 2010); however, the clustering of symptoms within a 12-month period was not imposed. This decision was based on findings from a previous analysis of these data that found a genetic correlation of 0.99 for alcohol dependence (AD) symptom count with a separate measure of symptom clustering, indicating that clustering contributed almost no additional genetic information (Grant et al. 2009). That study also found a genetic correlation of 0.96 for AD symptom count and alcohol abuse, suggesting that abuse and dependence symptoms tapped the
