Participants were recruited primarily from the Mid-South states of Tennessee, Mississippi, and Arkansas during 1999-2004. Extensive clinical and medical data were collected on each participant, including demographics (e.g., sex, age, race, biological relationships, weight, height, years of education, and marital status), medical history, smoking history and current smoking behavior, ND, and other relevant personal characteristics. The enrollment criteria for proband smokers were: 1) at least 21 years old, 2) smoker for at least five years, 3) consumer of an average of 20 cigarettes per day during the last 12 months, and 4) free of a self-reported history of diagnosis of any serious mental disorder; e.g., schizophrenia or other psychosis, bipolar disorder, or cognitive disorder (such as dementia or Alzheimer’s disease). Once a proband was recruited, siblings and parents were invited to join the study whenever possible. All participants provided informed consent; the study protocol and forms/procedures were approved by all participating Institutional Review Boards.
