Abercrombie, D.
(1967). Elements of General Phonetics. Chicago: Aldine Publishing Co.
2.
Anderson, T. (1939). Variations in the Normal Range of Children's Voices, Variations in the Range of Tone Audition, Variations in Pitch Discrimination. Unpublished Ph.D. Thesis, University of Edinburgh.
3.
Bentley, A.
(1968). "Monotones": A Comparison with "Normal" Singers in Terms of Incidence and Musical Abilities. Music Education Research Papers No. 1. London: Novello.
4.
Fieldhouse, A. E. (1937). A Study of Backwardness in Singing Among Children. Unpublished Ph.D. Thesis, University of London.
5.
Gordon, E.
(1971). The Psychology of Music Teaching. Englewood Cliffs: Prentice Hall.
6.
Greene, M. C. L.
(1964). The Voice and its Disorders, 2nd edition. London: Pitman Medical Publishing Co.
7.
Gould, A. O.
(1965). The Development of Specialised Programs for Singing in the Elementary School. Bulletin of Council for Research in Music Education, No. 17, 9-22.
8.
Joyner, D. R. (1971). Pitch Discrimination and Tonal Memory and Their Association with Singing and the Larynx. Unpublished M.Phil. Thesis, University of Reading.
9.
Maxwell, A. E.
(1961). Analysing Qualitative Data. London: Methuen.
10.
Moses, P. J.
(1959). The Vocal Expression of Emotional Disturbance. Kaiser Foundation Medical Bulletin, 7, 107-111.
11.
Romaine, W. B. (1961). Developing Singers from Non-singers. Unpublished Thesis, Teachers College, Columbia.
12.
Tanner, J. M.
(1962). Growth at Adolescence, 2nd edition. Oxford: Blackwell.
13.
Tanner, J. M.
(1973). Sequence, Tempo and Individual Variation in Adolescent Growth and Development. In Westman, J. C. (Ed.). Individual Differences in Children. New York: Wiley.
