Adult Mental Illness Treat young girls who socialize with negative peers are more likely to experience depression in adolescence and also in adulthood.
An increase in one standard deviation of the proportion of female schoolmates, who are depressed, increases the probability of depression in adulthood by 2.6 percentage points for women.
It is the first study that provides a causal link of the impact of depression among peers in adolescence on their own depression later in adulthood.

School-aged girls who socialise with negative peers are more likely to not only experience depression during their youth, but are at an increased risk of mental health problems as adults, a world-first study by international economists has found
New research from Monash University and the University of Southampton shows depression can be contagious for teenage girls and have lasting effects into adulthood. It is the first study to causally link depression among peers in adolescence to depression occurring later in adulthood.
The study by Monash Business School’s Professor Yves Zenou and co-authors Dr Corrado Giulietti and Professor Michael Vlassopoulos from the University of Southampton, shows that just an increase in one standard deviation of the proportion of female schoolmates who are depressed, increases the probability of depression in adulthood by 2.6 percentage points for women.
Alarmingly, researchers found that an increase in peer depression by one standard deviation is also associated with a probability of college attendance that is 3.5 percentage points lower, a likelihood of working that is 2.8 percentage points lower, and a reduction in income of $1,870 annually.
The study uses data spanning 14 years from adolescence into early adulthood, of 12,400 individuals (6,663 females and 5,737 males) across 128 schools, from the US National Longitudinal Survey of Adolescent to Adult Health. Adult Mental Illness.
