of nondaily smokers. Individuals who start smoking at a later age perhaps become less dependent in general than those who start at a younger age.

Another atypical pattern of smoking that poses a quandary for tobacco prevention and control efforts is daily light smoking (i.e., smoking less than five cigarettes per day). Since 1993, data from NHIS show that the proportion of light smokers has increased from 2.9 percent in 1993 to 4.8 percent in 2004 (CDC 2005a). Although these light smokers (or “chippers”) may smoke daily, they do not develop nicotine dependence. They are, however, similar to dependent smokers on a number of parameters, including puff number and duration, as well as blood nicotine absorption and elimination levels. They also show cardiovascular responses similar to those of dependent smokers (Brauer et al. 1996; Shiffman 1989; Shiffman et al. 1990, 1992). These findings challenge classical theories of nicotine dependence (Shiffman 1989).

Studies that have examined the smoking attitudes and behaviors of smokers have also found perplexing similarities and differences between those of light smokers and those of dependent smokers. Presson and colleagues found that future chippers closely resembled future heavy smokers in viewing smoking as not very harmful to their health (Presson et al. 2002). Future chippers differed from heavy smokers, however, in that they had social environments with low levels of risk (i.e., low levels of smoking among peers and family members). Other studies have found that light smokers and heavy smokers tend to differ in their motives and attitudes toward smoking. Smoking behavior among light smokers tends to be influenced by social and sensory motives (the pleasure of handling cigarettes and smoking itself) rather than pharmacological or addiction-related reasons, such as cravings and habit (Shiffman et al. 1994). Notwithstanding the lack of classical nicotine dependence among low-level smokers, the scientific evidence on the harmful effects of exposure to low levels of nicotine (DHHS 2006) and the potential transitional nature of individuals in this subpopulation of smokers argue for focusing special attention on helping these individuals stop smoking.

A variety of individual and group characteristics and behaviors have been associated with higher rates of tobacco product use. Wallace (Appendix P) provides a review of some of these populations: adult smokers with mental illness, children and adolescents with mental illness and conduct disorders, inmates in correctional institutions, military recruits, homeless individuals, gamblers, and some individuals with disabling conditions.

Wallace notes that there have been a few recent national surveys suggesting that the majority of cigarettes in the United States are sold to per-