Sociodemographic characteristics should be considered potential environmental covariates in genetic research on cigarette use because the prevalence of smoking tends to be higher among disadvantaged groups. Additionally, disadvantaged users of cigarettes may be more likely to initiate use, less likely to be successful in quit attempts and face higher exposure to the harms of tobacco (46). Groups that are at higher risk for smoking include the poor, semi-skilled manual occupation groups, the unemployed, poor educational achievers, and single mothers (12,47). Smoking prevalence among these groups may be due to reduced support for quitting, low motivation to quit, stronger addiction to tobacco, targeted marketing by tobacco companies, and psychological differences regarding self-efficacy in the ability to quit (46), which could be intensified by high feelings of anxiety (48), hopelessness, lack of social, communication, and refusal skills, and low-self esteem (49), or experiencing highly stressful events in childhood (50). These are all potential points of intervention for cessation efforts and have the potential to reduce health costs associated with cigarette use. Cigarette use also varies by sex between countries, making it difficult
