Longitudinal study of friendships and enmities in middle school

We study the temporal evolution of friendships among teenagers during two consecutive academic years with five waves of a survey. Our results show a large degree of consistency among waves, which is remarkable in view of the fact that the studied period includes a major reorganisation of the school due to the COVID-19 pandemic. We show that the first two circles, best friends and friends, can be clearly observed in the survey but also that being in one or the other leads to more or less stable relationships. We have also studied enmities, finding that they are reported to a much lesser extent and are highly volatile. We find that being in the same class is one of the key drivers of friendship evolution. We also observe an almost constant degree of reciprocity in the relationships, around 60%, a percentage slightly influenced by being in the same class and gender homophily. Not only do our results confirm the mounting evidence supporting the layered structure of human social networks, but they also show that these structures persist in time despite the turnover of individual relationships -- a fact that may prove particularly useful for understanding the social environment in high schools.