1. The Teaching Problems of 1075 Public School Teachers
2. Robert Thorndike and Elizabeth Hagen , Measurement and Evaluation in Psychology and Education, New York: John Wiley and Sons, Inc., 1955, pp. 421-489.
3. Thomas H. Briggs and Joseph Justman, Improving Instruction Through Supervision, New York: The Macmillan Company, 1952, pp. 23-43.