Major Morbidity Mental retardation		The American Association of Mental Retardation defines MR as "a disability characterized by significant limitations in both intellectual functioning and adaptive behaviors, with these limitations originating before age 18." Adaptive behavior consists of conceptual, social and practical skills that are used in daily life. They can be evaluated by teacher or parent questionnaire or specific standardized tests. Intelligence can be measured using standardized tests administered by a trained professional. Before school-age, this is usually done with the Bayley Scales of Infant Development, now in its second edition. The Bayley consists of 2 scales, which can be converted to standard indices with a mean of 100 and standard deviation of 15 - the Mental Developmental Index (MDI) and the Psychomotor Developmental Index (PDI). Ordinarily, the preschool child with an MDI/PDI < 70 is referred to as having developmental delay. For school-aged children, standardized intelligence quotient (IQ) tests, like the Wechsler Intelligence Scale for Children-Revised (WISC-R), have a normal range defined as 2 standard deviations above/below the mean. By convention, the mean IQ is 100 with a standard deviation of 15. (Most IQ tests also have a standard error of 5 points.) Therefore the IQ scores that correspond to degrees of MR are: IQ > 85 Normal 70-85 Borderline MR 55-70 Mild MR 40-55 Moderate MR 25-40 Severe MR IQ < 25 Profound MR The great majority of children with an IQ < 70 have mild MR. Most can read at a 4th to 5th grade level. As teenagers, they often pursue vocational training to prepare them for semiskilled jobs. Many live independently, marry and have children. It has been reported that pediatricians tend to have unrealistically low expectations for the work and social outcomes of their patients with mild MR. Return to top of page