distribution. Finally, these analyses model age as a series of ordinal developmental periods (adolescence age 12-17, early adulthood age 18-25, adulthood age 26+), rather than a continuum. This approach is not sensitive to differences in genetic liabilities that may exist within the specified developmental periods; for example, the 18-25 age group includes subjects who cannot drink legally (< age 21) and others who can drink legally (> age 21) in Add Health and COGA. The legal drinking age in the U.K. (ALSPAC) is 18, further increasing heterogeneity in this analysis. Modeling age as a continuum, rather than discrete groups, may identify additional differences in genetic liabilities within these age groups.
