1. Kershaw, J.D. (1961) Handicapped children. William Heinemann. Medical Books Limited, London. p. 207.
2. Nigeria Census (1963) In Annual Statistical Bulletin, 1969, p. 7. Ministry of Health, Western State of Nigeria.
3. Ewing, A.W.G. and Ewing, E.C. (1964) Teaching deaf children to talk. University of Manchester Press, Washington, D.C., 7. p. 127.