Mild mental retardation in Gothenburg children born between 1966-70. Changes between two points of time

Changes between two points of time in prevalence rates and distribution of IQ values in mentally retarded children resident in Gothenburg, Sweden, and born between 1966-70 were analysed. The children at the first census date in 1978 were aged 8-12 years and at the second in 1984 aged 14-18 years. The population-based prevalence rates were 3.7 per 1,000 in 1978 and 3.9 in 1984 for mild mental retardation (MMR; IQ 50-70) and 3.0 and 3.3 respectively for severe mental retardation (SMR; IQ less than 50). The majority (82%) of the MMR children remained on the same intellectual and educational level. The changes that occurred were mainly downwards. Thirteen of the 91 MMR children in the 1978 series demonstrated IQ values below 50 by 1984. Ten of these 13 children had a clear biomedical origin for their retardation, e.g. six with cerebral palsy syndromes. The IQ level of three MMR children had improved to 71-85. Nineteen newcomers were identified as MMR. 14 of these had IQ test scores above 70 in 1978 including one with cerebral palsy and 5 with minimal brain dysfunction syndromes. The prevalence of children registered in the Board for Provisions and Services to the Mentally Retarded, all IQ categories included, increased from 6.7 per 1,000 in 1978 to 8.1 in 1984. One third of this increase was due to the greater recording of youths with an IQ above 75.