Courses of development in mentally retarded persons.

A total of 80 subjects, 47 of them men and 33 women, with an average age of 25 and an average IQ of 53, were studied using a wide range of psychological methods from 1966 to 1971. In addition data from the subjects' childhood was collected, including IQ, achievement at elementary school and certain social variables. Thirteen years later a follow-up study was carried out. All eighty subjects were traced and the attained social adjustment was analysed from a broad angle, combining quantitative and qualitative methods in the collection of data. In a proceeding longitudinal analysis the intention is to identify, describe and explain fundamental courses or processes of development, focusing both continuity and change over time. The results show that prediction is comparatively feasible as regards cognitive abilities and especially verbal and numerical skills, but considerably more difficult when it comes to more complex abilities. As regards changes and their causes only preliminary results are reported.