1. 2. A. Kankkunen Pre-school children with impaired hearing in Goteborg 1964-80. Diss. Acta Otolaryngol Univ. of Goteborg1982 .
2. 3. D Harvey, M Miles, and D. Smyth Community child health and paediatrics. Oxford:Butterworth Heinemann, 1995 :482 .
3. 4. M. Westerlund Barn med tal-och sprakavvikelser. En prospcktiv longitudincll epidemiologisk studie av en arskull uppsalabarn vid 4, 7 och 9 ars alder. [Children with speech and language deviations. A prospective longitudinal epidemiological study of a total age cohort of children living in Uppsala at 4, 7 and 9 years of age] Uppsala: Department of Paediatrics, Uppsala University, 1994 .
4. 5. C Gillberg, and L. Hellgren, Barn och ungdomspsykiatri [Child and youth psychiatry] . Stockholm:Natur och kultur, 1990 :155 .