may motivate smoking behaviour in adults. A similar study suggested that individuals may play a more active role in starting to smoke than has previously been thought and that social processes other than peer pressure also need to be taken into account. Another study's results indicated that peer pressure was significantly associated with smoking behavior across all age and gender cohorts, but that intrapersonal factors were significantly more important to the smoking behavior of 12- to 13-year-old girls than same-age boys. Within the 14- to 15-year-old age group, one peer pressure variable emerged as a significantly more important predictor of girls' than boys' smoking. It is debated whether peer pressure or self-selection is a greater cause of adolescent smoking. Psychologist Hans Eysenck (who later was questioned for nonplausible results and unsafe publications) developed a personality profile for the typical smoker. Extraversion is the trait that is most associated with smoking, and smokers tend to be sociable, impulsive, risk taking, and excitement seeking individuals. Persistence The reasons given by some smokers for this activity have been categorized as addictive smoking, pleasure from smoking, tension reduction/relaxation, social smoking, stimulation, habit/automatism, and handling. There are gender differences in how much each of these reasons contribute, with females more likely than males to cite tension reduction/relaxation, stimulation and social smoking. Some smokers argue that the depressant effect of smoking allows them to calm their nerves, often allowing for increased concentration. However, according to the Imperial College London, "Nicotine seems to provide both a stimulant and a depressant effect, and it is likely that the effect it has at any time is determined by the mood of the user, the environment and the circumstances of use. Studies have suggested that low doses have a depressant effect, while higher doses have stimulant effect." Patterns A number of studies have established that cigarette sales and smoking follow distinct time-related patterns. For example, cigarette sales in the United States of America have been shown to follow a strongly seasonal pattern, with the high months being the months of summer, and the low months being the winter months. Similarly, smoking has been shown to follow distinct circadian patterns during the waking day—with the high point usually occurring shortly after waking in the morning, and shortly before going to sleep at night. Effects Health Tobacco smoking is the leading cause of preventable death and a global public health concern. There