Adolescence and young adulthood are times of significant life change and stress. They are also key stages for brain development. Events that occur prior to or during these stages may contribute to later development of mental illness. Studying the relationship between stressful experiences at these ages and whether or not those who experience them go on to have psychotic experiences could help explain why people experience psychosis at all, and why some of those who could be considered to be ‘at risk’ of mental illness (due to life circumstances or genetics) go on to develop mental illness, while others do not. This study will look at data previously gathered from one group of adolescents and another of young adults, to try and measure how much stress these participants have experienced in their lives, and whether or not these experiences could be used to predict whether they would go on to to have psychotic experiences or other signs of mental illness.