1. Bleeker-Wagemakers EM 1981 On the causes of blindness in the mentally retarded. Bartimeus Foundation Thesis Amsterdam University
2. Mentally retarded in Denmark. An epidemiological study of 21.000 registered cases. Some results of a census, May 1974;Dupont;D Med Bull,1975
3. Severe mental retardation in children in a northern Swedish county;Gustavson;J Ment Defic Res,1977