In the study of nicotine dependence, it is important to understand the behavioral progression to nicotine dependence when choosing a control group. Subjects who have not had adequate nicotine exposure (ie, who have not smoked enough cigarettes) have not had the opportunity to become nicotine dependent. For this reason, genetic studies of nicotine dependence carefully choose for their control group regular smokers who did not become nicotine dependent. This choice minimizes the possibility that the controls would become dependent if they had adequate nicotine exposure.
