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Mental illnesses largely involve alterations in mood, thinking, and behaviour, as well as other domains of mental functioning, and affect almost all Canadians in some way, either directly or indirectly.1 They routinely cause significant impairments in emotional functioning, which may lead to social or physical limitations. In some cases, such as in agoraphobia, individuals cannot even leave their homes due to intense anxiety; depression can cause an individual to lose all interest in life. What further complicates mental illnesses is that they are often comorbid with other mental illnesses.

Mental illnesses have a substantial impact on quality of life. Although they are only responsible for 1% of deaths worldwide, mental illnesses account for almost 11% of the disease burden.2 In fact, of the ten leading causes of years lost due to disability in the world, mental illnesses accounted for four: major depression was ranked number one, alcohol use disorders was ranked second (among males), schizophrenia was fifth among males and sixth among females, and bipolar disorder was seventh among males and eighth among females.3 In Canada, the estimated economic burden of mental illness was $51 billion in 2003;4 these estimates include both direct and indirect costs.

This document describes the mental illnesses that have the greatest impact on Canadians in terms of prevalence or severity of disability. It also discusses how they affect the health status of Canadians. As part of a larger project, ICD9 codes were predominantly used in assessing information/collecting data for these health states as they were used to classify the diseases. The ICD9 codes are therefore presented for each condition if one is assigned.5 ICD10 codes are additionally provided for reference.6 The Diagnostic and Statistical Manual of Mental Disorders (4th revision)7 was also consulted for each disorder; the DSM-IV provides diagnostic criteria for each psychiatric disorder.

Affective disorders, which are disturbances primarily in mood, will be described. Of these, major depression, dysthymia, and bipolar affective disorder are included. Anxiety disorders, which cause intense and often persistent anxiety, will also be described, including panic disorder, agoraphobia, social phobia, generalized anxiety disorder, obsessive-compulsive disorder, and post traumatic stress disorder.

Childhood conditions (attention-deficit/hyperactivity disorder, pervasive developmental disorders, including autistic disorder and Asperger's disorder, and separation anxiety disorder), are also described. The functional limitations associated with eating disorders, including anorexia nervosa and bulimia nervosa, are examined. Mental retardation in its mild, moderate, and severe cases is also described. It is important to note that although intellectual disability is the currently recognized/accepted, less stigmatizing phrase for mental retardation, this document refers to the medical condition according to the ICD9 and DSM-IV; therefore, we maintain the clinical terms for these descriptions.

The health state associated with an individual with a personality disorder is examined. Schizophrenia is a disorder of distorted thought and perception. The functional limitations caused by these subtypes are captured here: catatonic, paranoid, disorganized, undifferentiated, and residual schizophrenia.

Finally, the health states associated with disorders caused by substance use, including alcohol, heroin, benzodiazepine, cannabis, and stimulant use will also be described in terms of stages throughout the course of the disorder; specifically, the health states associated with chronic use, treatment, remission, and in some cases, overdose are examined. Coma is often a sequela to overdose but its health state will not be described in this document; the health state associated with coma will be presented in the Neurological document in this series.

Quite often, mental illnesses are comorbid with other mental illnesses. However, measuring comorbidity is a complex task and therefore was not considered in this text. Consequently, the health states and attribute levels described in this document address only those specific to the mental illness being discussed, in the absence of a comorbid disorder. Attribute levels assigned to each health state were scored using CLAMES (see Context at the beginning of this document). Compared to other scoring systems (e.g., HUI, EQ-5D), CLAMES is particularly strong in that it captures impairments in social relationships, a common limitation among individuals with mental illnesses. That being said, CLAMES is a general scale for measuring quality of life and is unable to capture other areas of functioning associated with some mental illnesses. For example, individuals who experience mania, as seen in bipolar disorder, are not scored according to the functional limitations associated with euphoria, since CLAMES captures depression in its emotional scale, rather than happiness. This limitation is addressed where necessary.

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