It is important to understand how cigarette use has been measured before getting into details about how we can determine how much of cigarette use is attributed to genes, the environment, and their interactions. The most common phenotypic measures of cigarette use include: initiation; adolescent smoking; cigarettes per day; regular smoking; nicotine dependence; and smoking cessation. Initiation is usually a self-report measure that is assessed using a yes or no question, such as “Have you ever smoked an entire cigarette?” (7). Although adolescent smoking is often treated as binary (yes/no) variable, the way in which it is assessed differs across studies. One study may measure adolescent smoking by asking the question, “Have you ever smoked (or tried smoking)?” to which adolescents can respond either yes or no (8). While another study may ask adolescents to choose from a nine-point scale with multiple response categories, ranging from “I have never smoked, not even one puff” to “I smoke at least once a day” and recode responses to either no (non-smoker) to yes (smoker) (9,10). There is also some variation in how
