Adolescents who watch movies in which actors smoke a lot are about three times more likely to take up the habit than those exposed to less smoking on screen, new research suggests.

　　Some experts say the study published yesterday on the Website of The Lancet medical journal provides the strongest evidence to date that smoking depicted in movies encourages adolescents to start smoking, while others say they remain unconvinced.

　　Many studies have linked smoking in films with increased adolescent smoking, but this is the first to assess children before they start smoking and track them over time.

　　The investigators concluded that 52 percent of the youngsters in the study started smoking entirely because of seeing movie stars smoke on screen.

　　"This effect is stronger than the effect of traditional cigarette advertising and promotion, which accounts for 'only' 34 percent of new experimentation," said Stanton Glantz, a professor of medicine at the Institute for Health Policy Studies at the University of California in the United States, who was not connected with the research.

　　The research, conducted by scientists at Dartmouth Medical School in the US, involved 2,603 children from schools of US states of Vermont and New Hampshire who were aged between 10 and 14 at the start of the study in 1999 and had never smoked a cigarette at the time they were recruited.

　　The adolescents were asked at the beginning of the study which movies they had seen from a list of 50 movies, hits released between 1988 and 1999.

　　Investigators counted the number of times smoking was depicted in each movie and determined how many smoking incidents each of the adolescents had seen. Exposure was categorized into four groups, with the lowest level involving between zero and 531 occurrences of smoking and the highest level involving between 1,665 and 5,308 incidents of smoking. There were about 650 adolescents in each exposure group.

　　A year or two later, 259, or 10 percent, of the youths reported that they had started to smoke.

　　Twenty-two of those exposed to the least on-screen smoking took up the habit, compared with 107 in the highest exposure group. That was a five-fold difference.

　　However, after taking into account factors known to be linked with starting smoking, such as sensation seeking, rebelliousness orshavingsa friend or family member who smokes, the real effect was reduced to a three fold difference.