The Mental deficiency reference article from the English Wikipedia on 24-Apr-2004
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Mental deficiency

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Mental deficiency is the condition of a person deemed to possess a level of intellectual capacity that is so far below normal as to seriously impact the individual's ability to function in society.

The three traditional terms denoting varying degrees of mental deficiency long predate psychiatry. They were originally used in English as simple forms of abuse, and this is still the main usage. Their now obsolete use as psychiatric technical definitions is of purely historical interest. There have been some efforts made among mental health professionals to discourage use of these terms.

Idiocy indicated the greatest degree of mental deficiency, where the mental age is 2 years or less, and the person cannot guard himself against common physical dangers. The term is gradually being replaced by the term profound mental retardation.

An 'idiot' is the corresponding term for a person affected by idiocy. Similarly, the terms imbecile and moron once had scientific definitions that have now been superseded.

Imbecility was a type of mental deficiency less extreme than idiocy and not necessarily inherited. It is now usually subdivided into two categories, known as severe mental retardation and moderate mental retardation.

Moron was defined by the American Association for the Study of the Feeble-Minded in 1910, following work by H. H. Goddard, as the term for an adult with a mental age between eight and twelve; mild mental retardation is now the more widely-accepted term for this condition. Alternative definitions of these terms based on IQ were also used. For example, the following data based on the Wechsler adult IQ test (WAIS) were used in 1958:

Idiotbelow 20
Borderline deficiency70-79

Today the following ranges are in standard use:

Profound mental retardationbelow 20
Severe mental retardation20-34
Moderate mental retardation35-49
Mild mental retardation50-69
Borderline deficiency70-79

The word idiot comes from the Greek word ιδιωτης, idiôtês, "a private citizen, individual", from ιδιος, idios, "private". In ancient Athens, an idiot was a person who declined to take part in public life, such as democratic city government. Since such activities were honorable and could directly affect all citizens, idiot was a term of derision.