Laursen tracked 573 seventh-grade two-person friendships until they ended or until 12th grade. A few important behavioral traits emerged as predictors of friendships that lasted more than a year: popularity, aggression and academic success. The more similar two friends were in these traits, the longer a relationship lasted.

劳尔森跟踪了573对七年级的友谊关系，到第十二个学年结束或是持续到第十二个学年。其发现了一些预示着友谊关系持续一年以上的重要的行为特征：知名度、上进心、和学业成绩。两个朋友在这些特征上越相似，友谊关系将维持地越长久。

Friends of the opposite sex were least likely to last. “They're completely doomed,” Laursen says, in part because of pressure from other friends. Adolescents tend to sort themselves based on age, race and gender, so being friends with a member of the opposite sex limits the size of one's larger group of “running buddies” and taxes the relationship.

异性朋友之间的关系维持下去的可能性最小。劳尔森称：“他们注定是要终结的”，部分原因可能是来自于其他朋友的压力。青少年倾向于将朋友按年龄、种族和性别等因素予以分类，因此，和异性交朋友会限制自己扩大“同类好朋友”朋友圈，并且会给此种友谊造成负担。

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