A number of study limitations should be noted. Despite the large representative samples, estimates are based on self-report and lack the more detailed assessments of symptoms and diagnoses in clinical studies. Among younger samples, particularly adolescents, many individuals have not reached critical ages for dependence symptoms. Numerous other factors that could influence symptom reports were beyond the scope of this study (e.g., differences in comorbid conditions, age at drinking onset, family structure or family intactness, history of alcoholism). Despite the application of standardized DSM-IV criteria for alcohol use disorders, care must be taken when making comparisons with other studies. Aside from differences in sample selection, variations in measurement of the criteria and in the functioning of symptom items may contribute to observed differences with other studies.
