The Charles E. Schmidt College of Science study has found that teenage friendships end because of undesirable characteristics of friends and differences between friends or both, suggesting "birds of a feather flock together."
The study tracked friendships over the course of six years, measuring the effect of both dissimilarities and undesirable individual attributes in predicting when an adolescent friendship would end. Researcher Brett Laursen said that their study suggested that compatibility is a function of similarity between friends rather than the presence or absence of a particular trait. Participants of the study attended two middle schools in lower-middle and middle-class neighborhoods in a small city in the northeastern United States.
Fewer than 1 in 4 friendships that started in the seventh grade were maintained across the next school year and fewer than 1 in 10 friendships that started in the seventh grade survived the transition from middle school to high school. Only one percent of friendships that began in the seventh grade continued to the 12th grade.
The strongest predictors of friendship dissolution were differences in sex, differences in the degree to which children were liked by other children, differences in physical aggression, and differences in school competence. By far the strongest predictor was differences in sex, other-sex friendships were almost four times more likely to dissolve than same-sex friendships.
The next strongest predictor was differences in physical aggression, followed by differences in school competence, and differences in being liked by other children.
Laursen said that dissimilarity was bad for friendships, adding that it causes conflict, it interferes with cooperative activities and shared pleasures, and it creates circumstances where one friend bears more costs, such as the friend who is less aggressive or gets more benefits. The study is published in the journal Psychological Science