Are American children more susceptible to severe mental illness now than in the past? It depends whom you ask. A new study suggests the proportion of young people with the poorest mental health has declined over the past decade. The findings, published yesterday in The New England Journal of Medicine, contradict figures from national surveys indicating that more children than ever have mental health problems. “The finding is robust and real and challenges the prevailing stereotype that young people are somehow more vulnerable to mental problems,” Mark Olfson, professor of clinical psychiatry at Columbia University, told The New York Times.