Poor mental health among children and young people has been described as an epidemic and an "escalating crisis".
The number of children seeking help from Child and Adolescent Mental Health Services (Camhs) in England, has more than doubled over the past two years.
But establishing how much of this represents an actual rise in young people experiencing problems, and how much is down to better awareness of symptoms and diagnosis, is difficult.
Staying with England for now, our best shot is to look at a representative sample of the whole population, not just those who have come in contact with mental health services.
An NHS survey of young people in England, selected from GP records, did just this.
It found a small but genuine rise in diagnosable emotional disorders like depression and anxiety, especially among girls.