The study by researchers from the University of Southern California (USC) identifies how friends' and parental influence on cigarette smoking changes from junior high to high school.
The research indicates that intervention targets to counteract friends' influence may have more of an effect in junior high than in high school, and that parents remain influential on smoking behavior through high school, indicating another possible intervention target, the researchers said.
"Based on social developmental model research, we thought friends would have more influence on cigarette use during high school than junior high school," first author Yue Liao, M.P.H., Ph.D., a student in the department of preventive medicine's Institute for Health Promotion and Disease Prevention Research (IPR) at the Keck School of Medicine of USC, said.
"But what we found was friends have greater influence during junior high school than high school. We think the reason may be that friends' cigarette use behavior may have a stronger influence on youth who start smoking at a younger age. During high school, cigarette use might represent the maintenance of behavior rather than a result of peer influence," Liao said.
The full trial followed adolescents from age 11 to adulthood, specifically age 37.
Participants were first observed in the seventh grade - during junior high school - and then again after six months, and then annually through the 12th grade, during high school.
Students were asked to indicate the number of close friends and parents, or two important adults, who smoked cigarettes.
They were also asked how many cigarettes they had smoked in the last month.
The effects of friends' and parents' cigarette use on self-use were assessed from early to late adolescence in order to identify changes in trends and magnitude.
Results confirmed that overall, both friends' and parental cigarette use had significant effects on adolescents' cigarette use during both junior high school and high school.
However, while friends' influence was generally higher in junior high school than in high school, parental influence remained relatively stable between these two periods, with a decreasing trend from 10th to 12th grade.
This finding confirms previous research that suggests social units, such as school or community, may exert more influence on youth behavior than parents in high school.
The researchers also observed gender differences in friends' and parental influence. Friends' influence on cigarette smoking was greater for girls than boys during ninth and 10th grade.
However, there was an increasing trend in friends' influence from ninth to 11th among boys whereas friends and parents had less influence on girls from 10th to 12th grade.
The study is published in the Journal of Adolescent Health.