Two longitudinal studies of the abilities of people with Down's syndrome.

A cohort of subjects with Down's syndrome born in South Wales, UK, in 1964, 1965 and 1966, and living at home, was studied as infants, teenagers and young adults (the original cohort). Carers were interviewed and the abilities of the subjects assessed, using a variety of measures. Average scores of the cohort improved over the years, although the rate of progress slowed down between the teenage and adult years. Scores were related to social class, stimulation given in the home, and at older ages, maternal age at the birth of the subject. This latter finding was unexpected. A comparative cohort of subjects with Down's syndrome from South Wales born in 1973, 1974 and 1975 was studied as infants and teenagers. They were at the same stage as the original cohort as infants and teenagers, but living 9 years later. In spite of the comparative cohort coming from a favoured background, in terms of social class and having access to improved services, mean scores at the teenage stage were only significantly better on one test of language than those of the original cohort at the same age. Most studies find that females with Down's syndrome have higher abilities than males: this was the case for the original cohort, but not for the comparative cohort.