1. 1. H. Blomquist Mental retardation in children. Umea University Medical Dissertations. New Series No. 76, 1982 .
2. 3. Jordan Ministry of Social Development: Survey on mental retardation, 1979 .
3. 4. CA. Saunders A study of the prevalence of handicapping conditions affecting children in the refugee camp population of the Ghaza strip. Report from the Faculty of Education, University of Calgary, 1984 .