Alcohol use disorders (AUD) are common, complex disorders, the risk for which is contributed by genetic differences, environmental differences, and their interactions. AUDs lack an objective test. The current clinical definition (The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition; DSM-5) requires meeting at least 2 out of 11 criteria that reflect problems caused by consuming alcohol (American Psychiatric Association, 2013). The checklist definition means that theoretically one can meet DSM-5 criteria for AUD in 2036 different ways. Many studies have used DSM-IV definitions of alcohol dependence (AD; 3 or more of 7 criteria), which is more severe than a minimal DSM-5 definition, but still heterogeneous (99 possible combinations). This heterogeneity has obvious implications for the study of AUD. The requirement for alcohol consumption adds additional complexity, because there are large environmental differences in access to and acceptance of alcohol in different social groups and across time and location, and these can vary even within an individual’s life. Average drinks per week is widely studied, but is highly skewed, with most people consuming less than 2 drinks per week
