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Validity of the Discrimination Index as a Measure of Item Quality

Fred Pyrczak
Journal of Educational Measurement
Vol. 10, No. 3 (Autumn, 1973), pp. 227-231
Stable URL: http://www.jstor.org/stable/1434065
Page Count: 5
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Validity of the Discrimination Index as a Measure of Item Quality
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Abstract

Numerous writers have suggested that the discrimination index may be helpful in identifying faulty test items. The purpose of this study was to investigate systematically the validity of the index for this purpose. To attain this objective, two forms of an arithmetic-reasoning test were written. In each form, the items were designed to vary in quality with respect to nine item-writing principles, and on the basis of the responses of 364 examinees, a discrimination index was computed for each item. Next, the items were rated independently for quality by three judges who used a check list of the nine item-writing principles. The average of their ratings for each item was used as the criterion for determining the validity of the indices. The results indicate that the discrimination index is a moderately valid measure of item quality. The implications of this finding are discussed.

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