smokers need nicotine to remain feeling normal. In the mid-20th century psychologists such as Hans Eysenck developed a personality profile for the typical smoker of that period; extraversion was associated with smoking, and smokers tended to be sociable, impulsive, risk taking, and excitement-seeking individuals. Although personality and social factors may make people likely to smoke, the actual habit is a function of operant conditioning. During the early stages, smoking provides pleasurable sensations (because of its action on the dopamine system) and thus serves as a source of positive reinforcement. After an individual has smoked for many years, the avoidance of withdrawal symptoms and negative reinforcement become the key motivations. Like all addictive substances, the amount of exposure required to become dependent on nicotine can vary from person to person. In terms of the Big Five personality traits, research has found smoking to be correlated with lower levels of agreeableness and conscientiousness, as well as higher levels of extraversion and neuroticism. Prevention Education and counselling by physicians of children and adolescents has been found to be effective in decreasing the risk of tobacco use. Systematic reviews show that psychosocial interventions can help women stop smoking in late pregnancy, reducing low birthweight and preterm births. A 2016 Cochrane review showed that the combination of medication and behavioural support was more effective than minimal interventions or usual care. Another Cochrane review "suggests that neither reducing smoking to quit nor quitting abruptly results in superior quit rates; people could therefore be given a choice of how to quit, and support provided to people who would specifically like to reduce their smoking before quitting." Prevalence Smoking, primarily of tobacco, is an activity that is practiced by some 1.1 billion people, and up to 1/3 of the adult population. The image of the smoker can vary considerably, but is very often associated, especially in fiction, with individuality and aloofness. Even so, smoking of both tobacco and cannabis can be a social activity which serves as a reinforcement of social structures and is part of the cultural rituals of many and diverse social and ethnic groups. Many smokers begin smoking in social settings and the offering and sharing of a cigarette is often an important rite of initiation or simply a good excuse to start a conversation with strangers in many settings; in bars, night clubs, at work or on the street. Lighting a cigarette is often