1. Abelson, Harold H. “The Improvement of Intelligence Testing,” Contributions to Education, No. 273, New York: Teachers College, Columbia University, 1927. Obtained a consistency correlation with McCall’s coefficients of .279 ± .099 using 40 items.
2. Barthelmess, H. M. “The Validity of Intelligence Test Elements,” Contributions to Education, No. 505, New York: Teachers College, Columbia University, 1931. Using ten methods for obtaining indices, she found consistency correlations of .893 down to .548 with 25 items, 98 pupils vs. 262 pupils “including the 98.”.
3. Brigham, C. C. “A Study of Error,” New York: College Entrance Examination Board, 1932. His data gave a consistency value of .28 by computing the rank correlation between two sets of validity coefficients for the same 15 items.
4. Optimum difficulty of group test items.