In addition to the five traits discussed above, we also evaluated the nicotine dependence, alcohol dependence, and alcohol consumption phenotypes among individuals with adequate exposure to these substances. Nicotine exposure was defined as having done at least one of the following: smoked 2+ cigarettes on days they reported smoking or smoked 4+ days per month in the past year or having 1+ lifetime symptom(s) of dependence. Alcohol exposure was defined as having done one of the following: drinking at least once a month in the past year or ever having 6+ drinks in 24 hours or at least 2 lifetime intoxications or having 1+ lifetime symptom(s) of dependence. Minor modifications to these criteria resulted in only small fluctuations in the selected sample. Using these criteria, 3412 individuals from 1694 families were considered exposed to nicotine, and 5897 individuals from 2211 families were considered exposed to alcohol. We refer to these phenotypes throughout as nicotine (exposed), drinking (exposed), and alcohol dependence (exposed). We did not consider exposed versions of illicit drug use for several reasons, including the complex process of conditioning
