Mental deficiency is a cerebral tergimutation, and the afflicted exhibit, as a result, defective intelligence, retarded learning power and varying degrees of social maladjustment due either to unfavorable environment or to unfavorable personality traits or to both. Defective intelligence always carries with it retarded learning power and is therefore so important as to be considered fundamental and, whether regarded as mental age or as intelligence quotient, is the basis of classification and the guide to social adjustments. Mentally defective persons are classified as idiots (mental age, 0 to 3 years; intelligence quotient, 0 to 25), imbeciles (mental age, 3 to 7 years; intelligence quotient, 26 to 50), or morons (mental age, 7 to 12 years; intelligence quotient, 51 to 70 or 75). When the intelligence defect is sufficiently great, as in idiots and imbeciles, social adjustment is not possible, and the conduct of these persons will never be acceptable to
LAIRD A. MENTAL DEFICIENCY. Am J Dis Child. 1935;49(6):1607–1615. doi:10.1001/archpedi.1935.01970060211017
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