The Collaborative Genetic Study of Nicotine Dependence (COGEND), recruited participants from the St. Louis, Missouri and Detroit, Michigan, metropolitan areas. Both cases and controls were required to have smoked at least 100 cigarettes in their lifetime, a frequently used threshold to define being a smoker (e.g. CDC 2005). In addition to this criterion, subjects were ascertained based on their Fagerström Test for Nicotine Dependence (FTND) scores for their period of heaviest smoking (Heatherton et al. 1991). Cases were required to score 4 or higher, while controls were required to report never having symptoms of dependence (lifetime FTND = 0). Cases and controls were identified through a screening process in which telephone interviews on 54,644 individuals across the two sites were conducted (screening response rate= 74%). Among screened individuals, subjects were ineligible if they did not meet the requirements listed above, or were not within the targeted age range for the study (25–44 years). Among the 5,010 individuals meeting eligibility requirements, 3,137 were interviewed (response rate = 63%), and 2,949 donated a blood sample for genetic testing (response rate = 94%).
