What is the mental deficiency?

Mental deficiency takes into account three criteria: intellectual functioning significantly below average, the deficit of the adaptive behavior and the fact that the mental deficiency occurs during the development period.
In order for a person to be diagnosed with a mental deficiency, he or she must obtain an I.Q. below or equal to 70 at more standardized tests that measure general intelligence.
The second criterion is adaptive behavior deficit that relates to maturing and learning standards, to personal autonomy and social responsibility established for the age group and social group to which he/ she belongs.
The correlation between IQ and adaptive behavior measurements varies depending on the nature and type of adaptive behavior of the population studied. However, this correlation seems to be higher in profound mental disability. In subjects with a slightly mental deficit, the correlation is less clear, and in some subjects with an IQ around 70 we may not find a deficit of the adaptive behavior.
Mental deficiency should not be considered as a permanent situation as an individual may meet the criteria of mental deficiency in a moment of his life, but do not meet these criteria at another time.
For the mental deficiency diagnosis adaptive behavior assessment is therefore indispensable.
The third criterion of the definition refers to the fact that the lower IQ and the inadequate behavior must be present during developmental period that is between conception and 18 years old.
Mental deficiency is a global a insufficiency and an IQ below average, which is manifested by a stagnation a slowdown or a lack of purchasing in development, with adverse consequences on adaptive behavior.