Burden of Mental and Behavioural Disorders. (Chapter Two)

World Health Report, Annual 2001 | Go to article overview
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Burden of Mental and Behavioural Disorders. (Chapter Two)

Mental and behavioural disorders are common, affecting more than 25% of all people at some time during their lives. They are also universal, affecting people of all countries and societies, individuals at all ages, women and men, the rich and the poor, from urban and rural environments. They have an economic impact on societies and on the quality of life of individuals and families. Mental and behavioural disorders are present at any point in time in about 10% of the adult population. Around 20% of all patients seen by primary health care professionals have one or more mental disorders. One in four families is likely to have at least one member with a behavioural or mental disorder. These families not only provide physical and emotional support, but also bear the negative impact of stigma and discrimination. It was estimated that, in 1990, mental and neurological disorders accounted for 10% of the total DALYs lost due to all diseases and injuries. This was 12% in 2000. By 2020, it is projected that the burden of these disorders will have increased to 15%. Common disorders, which usually cause severe disability, include depressive disorders, substance use disorders, schizophrenia, epilepsy, Alzheimer's disease, mental retardation, and disorders of childhood and adolescence. Factors associated with the prevalence, onset and course of mental and behavioural disorders include poverty, sex, age, conflicts and disasters, major physical diseases, and the family and social environment.


Mental and behavioural disorders are understood as clinically significant conditions characterized by alterations in thinking, mood (emotions) or behaviour associated with personal distress and/or impaired functioning. Mental and behavioural disorders are not just variations within the range of "normal", but are clearly abnormal or pathological phenomena. One incidence of abnormal behaviour or a short period of abnormal mood does not, of itself, signify the presence of a mental or behavioural disorder. In order to be categorized as disorders, such abnormalities must be sustained or recurring and they must result in some personal distress or impaired functioning in one or more areas of life. Mental and behavioural disorders are also characterized by specific symptoms and signs, and usually follow a more or less predictable natural course, unless interventions are made. Not all human distress is mental disorder. Individuals may be distressed because of personal or social circumstances; unless all the essential criteria for a particular disorder are satisfied, such distress is not a mental disorder. There is a difference, for example, between depressed mood and diagnosable depression (see Figure 1.3).

Diverse ways of thinking and behaving across cultures may influence the way mental disorders manifest but are not, of themselves, indicative of a disorder. Thus, culturally determined normal variations must not be labelled mental disorders. Nor can social, religious, or political beliefs be taken as evidence of mental disorder.

The ICD-10 classification of mental and behavioural disorders: clinical descriptions and diagnostic guidelines (WHO 1992b) gives a complete list of all mental and behavioural disorders (see Box 2.1). Additional diagnostic criteria for research are also available for a more precise definition of these disorders (WHO 1993a).

Any classification of mental disorders classifies syndromes and conditions, but not individuals. Individuals may suffer from one or more disorders during one or more periods of their lives, but a diagnostic label should not be used to describe an individual. A person should never be equated with a disorder -- physical or mental.


Mental and behavioural disorders are identified and diagnosed using clinical methods that are similar to those used for physical disorders. These methods include a careful and detailed collection of historical information from the individual and others, including the family; a systematic clinical examination for mental status; and specialized tests and investigations, as needed.

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