1. Bluemel C. S. Stammering and Allied Disorders. New York Macmillan 1935.
2. Fisher R. A. Statistical Methods for Research Workers Sixth Edition. London Oliver and Boyd 1936.
3. Fletcher J. M. The Problem of Stuttering. New York Longmans Green 1928.
4. Guilford J. P. Psychometric Methods. New York McGraw-Hill 1936.
5. A statistical analysis of the adaptation and consistency effects in relation to stuttering;Johnson W.;Journal of Speech Disorders,1939