Discussion
Which of the following is/are used as item discrimination indices ?
(I) Phi-coefficient
(II) Point-Biserial correlation
(III) Spearman's Rho
Codes :
Answer: C
The item discrimination indices are (I) and (II) only.
Item discrimination shows how well an item separates high scorers from low scorers. When item scores are dichotomous (right or wrong), it is computed as a correlation between the item and the total or criterion score. The point-biserial correlation relates the dichotomous item to a continuous total score, and the phi coefficient relates the item to a dichotomised criterion (for example upper versus lower group). Both are standard discrimination indices.
Spearman's rho is a rank-order correlation between two sets of ranks, not used as an item discrimination index, so options including (III) are wrong.
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