also being a habitual smoker—that is, siblings of smoking alcoholic probands were at higher risks of smoking themselves than were siblings of nonsmoking alcoholic probands, indicating in part a specific familial transmission of habitual smoking. Siblings share many characteristics that may be risk factors for the development of alcohol dependence and smoking. The COGA investigators therefore analyzed the data to evaluate the effects of multiple potentially confounding characteristics on the risk of developing habitual smoking or alcohol dependence. According to these analyses, characteristics that strongly predicted an increased risk of alcohol dependence included the sibling’s gender, birth cohort, and history of other drug dependence, as follows (also see table 3):
