Diagnostic Criteria

In attempts to increase the reliability of psychiatric diagnoses, most classification systems have become 'operationalised' so that the criteria needed to make a particular diagnosis have become very specific and clear to minimise room for disagreement. DSM V has adopted this approach and allows for the systematic recording of clinical information. As noted, DSM V disorders are grouped into major diagnostic classes.  In general, these classes are based on groups of illnesses that share common symptoms or tend to occur at a particular developmental stage.  Within each major diagnostic class the specific criteria required to make a diagnosis are set out.  Usually this will consist of inclusion criteria (i.e. symptoms or factors that must be present to make the diagnosis) and exclusion criteria (i.e. symptoms or factors that, if present, dictate that a particular diagnosis cannot be made). Criteria are generally quite restrictive and specific. Although DSM V lists the criteria needed to make a diagnosis it does not attempt to include the total range of problems and symptoms that may co-exist with any one diagnosis.

As an example, here are the DSM-V diagnostic criteria for depression.

A.  Five (or more) of the following symptoms have been present during the same two-week period and represent a change from previous functioning; at least one of the symptoms is either (1) depressed mood or (2) loss of interest or pleasure. Note: Do not include symptoms that are clearly due to a medical condition. (1) depressed mood most of the day, nearly every day, as indicated by either subjective report (e.g., feels sad or empty) or observation made by others (e.g., appears tearful). Note: in children and adolescents can be irritable mood. (2) markedly diminished interest or pleasure in all, or almost all, activities most of the day, nearly every day (as indicated by either subjective account or observation made by others). (3) significant weight loss when not dieting or weight gain (e.g., a change of more than 5% of body weight in a month), or the decrease or increase in appetite nearly every day.  Note: in children, consider  failure to make expected weight gains. (4) insomnia or hypersomnia nearly every day. (5) psychomotor agitation or retardation nearly every day (observable by others, not merely subjective feelings of restlessness of being slowed down). (6) fatigue or loss of energy nearly every day. (7) feelings of worthlessness or excessive or inappropriate guilt (which may be delusional) nearly every day (not merely self-reproach all guilt about being sick). (8) diminished ability to think or concentrate, or indecisiveness, nearly every day (either by subjective account or as observed by others). (9) recurrent thoughts of death (not just a fear of dying), current suicidal ideation with  a specific plan, or a suicide attempt or a specific plan for committing suicide. B. the symptoms cause clinically significant distress or impairment  in social, occupational, or other important areas of functioning. C. the symptoms are not due to the direct physiological effects of a substance (e.g., a drug of abuse, medication) or a general medical condition (e.g. hypothyroidism). D The occurrence of the major depressive episode is not better explained by schizoaffective disorder, schizophrenia, schizophreniform disorder, delusional disorder or other psychotic disorders. E. There has never been a manic or hypomanic episode.

Before continuing, take a moment to consider what difficulties there may be in

categorising mental illness like this for people with intellectual disability.