Allemand, Steiger, and Fend (2015) performed a 23-year study to determine if adolescent empathy could predict outcomes in adulthood. 1,527 adults were given surveys every year from age 12 to 16, and again at age 35. The surveys given during adolescence asked participants to rate their ability to read other people's emotions. When tested at 25, they were given three of the same type of questions plus questions on their communication skills, social integration, romantic relationship satisfaction, and frequency of conflict within romantic relationships.
The authors found that most people increase in their ability to read others' emotions in adolescence and that girls tend to start at a higher level than boys but their empathy develops at approximately the same rate. They also found that not only those who ranked higher as a teen but also those who developed empathy at a faster rate during adolescence had more empathy and communication skills as an adult. The level of empathy as a teen did not predict social integration as an adult, but the relative change in empathy did: those who became more empathetic as an adolescent tended to feel less lonely as an adult. The measurements of romantic relationship satisfaction & conflict had no significant relationship with empathy during adolescence.
This study has a significant flaw in that it relies on self-reports to determine empathy skills, and that they used a tool of measurement which only contained 8 questions, all about reading other people's emotions (which is not even half of what empathy is). I think most of it is thus not useful, and the only thing I take away from this is that when people learn to read others' emotions during adolescence, they have an easier time forming community as an adult.
The authors also fail to notice that they've used a self-reporting measurement tool which asks about gendered behavior and assume that their findings agree with "stereotypes and popular culture" which assume that women have "greater capacity" for empathy than men. If these people had done their homework as responsible social scientists, they'd have learned that young girls are trained to do cognitive empathy tasks while boys are not, and they wouldn't make such a ridiculous assumption of different "capacity."
[reference]Allemand, M., Steiger, A. E. and Fend, H. A. 2015. "Empathy Development in Adolescence Predicts Social Competencies in Adulthood."Journal of Personality 83, no. 2: 229–241. doi:10.1111/jopy.12098