I wish to express my gratitude to the following people: • To God Almighty who gave me the courage and strength to complete this degree. • To my supervisor, Professor F.E. Gouws for her encouragement, support and guidance that she has provided throughout this study. • Mr H.J. Gerber for his expert advice and assistance with the statistical data. • To my parents for encouraging and supporting me. • To my mother in-law for her understanding and support