Studies in mental handicap. I. Prevalence and distribution by clinical type and severity of defect.

An aetiological study of mentally handicapped children in Edinburgh has provided an opportunity for assessing the prevalence of mental handicap in this area and the distribution of handicapped children by severity of defect and clinical type.A definite cause of mental handicap is found in only a minority of cases.Nevertheless, any aetiological investigation must begin with an attempt to classify patients by clinical condition, since associations of possible aetiological significance are likely to differ for those having subnormal intelligence only and those having different neurolo- gical or physical abnormalities in addition to sub- normal intelligence.In this study the term 'mentally handicapped' is applied to children who are considered unsuitable for education in ordinary schools primarily on account of subnormal intelligence (i.e.estimated intelligence quotients of less than 70), but not to dull and backward children who are educationally retarded and may, in certain circumstances, be ineducable in the normal school system.The Survey Sample Children selected for study were all those with IQ test scores below 70, born in the years 1950-56, who were themselves resident in Edinburgh and/or whose mothers were resident in Edinburgh in 1962-64.Names of children considered to be mentally handi- capped were obtained from registers compiled by the public health department and school medical service.Registers of children classified as physically handicapped were also scrutinized, since some mentally handicapped children may be so classified for domestic reasons.All voluntary day centres for handicapped children in Edinburgh were contacted, as were residential institu- tions and schools (both voluntary and state) for mentally and physically handicapped children throughout Scot- land.A final scrutiny of the relevant registers was made in July 1964, to include children who had been ascertained