Mild mental retardation in Swedish school children. I. Prevalence.

In an unselected series of Swedish school children born 1966-70, the prevalence of mild mental retardation, defined as an IQ of 50-70, was determined. A prevalence of 0.4% was revealed. The findings in this study, supported by recent IQ analyses in other Scandinavian countries, indicate that a true prevalence for the IQ range 50-70 was ascertained. The high average social standard and early social stimulation are put forth as a likely explanation for the low prevalence of mild mental retardation in Swedish preschool and school children.