Phenomenology Epidemiology Population based surveys across numerous countries and cultural groups have recorded the prevalence of mental health disturbance in children and adolescents at between 15 - 20%. Methodological and design issues include whether the research was primarily parent report which finds higher rates of externalising disorders; child and youth self-report which provides better estimates of internalising disorders; or more robust designs which included information from multiple informants. General trends include higher rates of externalising disorders in males and of internalising disorders in females. Often, as is the case with depression, gender-based rates are similar in the pre-pubertal period. Post-puberty rates of depression are higher in females. Some conditions present at specific developmental stages, for example early onset psychosis is rare before the middle teenage years, or demonstrate a clear developmental relationship or progression. An example of the latter is the common trajectory from oppositional defiant disorder (ODD) in children to conduct disorder in adolescents.
It is probable there are many reasons for cross-cultural differences in the prevalence of specific conditions. One is that the prevalence of illness/disorder will be influenced by local conditions; anorexia nervosa is more common in affluent developed world. Another is the willingness to diagnose depends on culture; what was naughtiness in some western societies is now ODD or ADHD. With these caveats in mind useful prevalence estimates include a rate and diagnosable depressive disorder of approximately 3%, anorexia nervosa 0.5%, ADHD 6%, ODD and CD 6-10% (increasing with age) and autism 0.1%. Note one cannot simply add these prevalence figures and conclude that most children have a mental health problem. Conditions are often comorbid with one individual sometimes experiencing two or three mental health disorders.
Another consideration is impairment. Many symptoms such as mild anxiety, brief lowered mood or nightmares after a traumatic event are often normal. Key to the diagnosis and subsequent management plan is the impairment in daily functioning. If symptoms interrupt the child’s family or peer relationships, or impede their ability to attend and take advantage of school and other activities i.e. if symptoms either prevent normal function or normal development, then the presentation is more serious and worthy of an intervention. One measure of impairment is the disability adjusted life years (DALY) methodology. A recent application of this methodology to the child and adolescent mental health area suggests the impairment burden of neuropsychiatric conditions in children will double by the year 2020.