An unselected general population sample of 147 individuals was recruited to assess phenotype base rates. Letters were sent to residents of the same geographical areas as the family samples, requesting participation in a study on “health behaviors and characteristics” to avoid a sample biased toward participation in a study on alcoholism. No inclusion/exclusion criteria were applied aside from the ability to respond to the telephone interview and complete the questionnaires. Within this population, 36 participants (24%) were diagnosed only with nicotine dependence, 14 (10%) were diagnosed only with alcohol dependence, and 11 (7%) were diagnosed with both disorders. The recruitment details of all participants have been previously published (Seaton et al., 2004; Vieten et al., 2004).
