In the initial assessment, the researchers did not evaluate the participants for nicotine dependence, but instead used habitual smoking as a proxy, which was defined as smoking 1 pack (i.e., 20 cigarettes) per day for at least 6 months. In a subset of study participants, however, the investigators conducted a full evaluation of nicotine dependence and found that 71 percent of habitual smokers also were nicotine dependent. The investigators used the information from the stage I sample to examine the risk of developing alcohol dependence or habitual smoking in families with alcohol-dependent members, as described in the following section.
