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2. Ebel, R.L.Essentials of Educational Measurement. Englewood Cliffs, NJ: Prentice Hall, 1979, pp. 252–255.
3. Hills, J.R.Measurement and Evaluation in the Classroom(2nd Edition). Columbus, Ohio: C.E. Merrill, 1981, pp. 320–324.
4. A CASE FOR PROFESSIONAL JUDGMENT WHEN COMBINING MARKS