Both causal and noncausal models may relate to national trends in cigarette consumption. Cigarette consumption, which reflects both the prevalence and the intensity of smoking, increased more than fivefold from 1920 to 1960, reached a plateau between 1965 and 1975, and has declined consistently since that time. At the peak around 1966, roughly one-half of men and one-third of women in the United States smoked regularly (Forey et al. 2007). Two changes took place during the 1960s and 1970s that had important implications for smoking. These changes first affected the direction of the social push from pro-smoking to antismoking, and later they causally affected the genetic influences on smoking by reinstituting social control. The first event occurred in 1964 when the Surgeon General released the first of a number of reports with clear warnings about the dangers of smoking. This led to the 1965 Federal Cigarette Labeling and Advertising Act, which required that all cigarette packages bear the Surgeon General’s Warning: “Caution: Cigarette Smoking May Be Hazardous to Your Health.” The first report focused on the link between smoking and
