 However, the number of smokers worldwide has increased from 721 million in 1980 to 967 million in 2012 and the number of cigarettes smoked increased from 4.96 trillion to 6.25 trillion due to population growth.In Western countries, smoking is more prevalent among populations with mental health problems, with alcohol and drug problems, among criminals, and among the homeless.In 2002, about 20% of young teens (aged 13–15) smoked worldwide.