Epidemiological data on youth mental health are fragmented. The use of standardized tools in self-report surveys makes it possible to address certain mental health issues and study their associated factors, even though these tools have numerous limitations. Globally, despite significant variations in results—largely due to differences in the methodologies used in the studies—the data indicate that approximately one-quarter of young people have experienced a mental health disorder in the past twelve months. The observed variations are sometimes due to genuine cultural differences. Anxiety and depressive disorders, as measured by standardized tools outside of a clinical setting, are the most common conditions among adolescents. The recent development of simple, effective, and validated tools specific to adolescents allows for improved monitoring of such disorders. A scale for measuring depressive severity, the Adolescent Depression Rating Scale (ADRS), has thus recently been validated in French and introduced into the Ecaap survey, as well as into the Espad survey conducted in France in 2007.[chapter excerpt]