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A Rationale for Evaluation of Item Discrimination Statistics

Findley, Warren G.
Publication Year:
Report Number:
ETS Research Memorandum
Document Type:
Page Count:
Subject/Key Words:
Item Analysis, Item Discrimination (Tests), Test Analysis, Test Items


A logical analysis and mathematical derivation have been presented that justify interpreting simple differences between upper and lower groups as reflecting precisely the relative effectiveness of discrimination achieved by items in a test. Also, it has been pointed out one may interpret the negative differences on wrong options in an item as measures reflecting precisely the relative contributions made by the distractive power of the several options to the positive difference found for the correct option. It is felt that these interpretations help clarify item analysis for the sophisticated test specialist as well as for the generally less sophisticated subject-matter specialists who are responsible in whole or in part for constructing classroom and standardized achievement tests.

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