Which of the following is/are true about the item discrimination index?
(I) It is a measure of reliability
(II) It is a measure of validity

Correct option is D

The item discrimination index is neither a measure of reliability nor validity. Instead, it is an item analysis statistic that indicates how well an individual item differentiates between test-takers who perform well on the overall test and those who perform poorly. It assesses the quality of individual test items, not the psychometric properties of the test as a whole. High discrimination indices suggest items that contribute effectively to the test's measurement precision.

Information Booster:
1. Definition: Discrimination index (D) typically ranges from -1.0 to +1.0, indicating the difference in performance between high and low scorers
2. Calculation: Often computed as the difference between the proportion of high scorers who answer correctly and the proportion of low scorers who answer correctly
3. Interpretation: Values above 0.30 are generally considered good; negative values indicate problematic items that should be revised or eliminated
4. Purpose: Helps identify items that effectively separate examinees with different ability levels
5. Item Analysis: Part of classical test theory's item analysis procedures along with item difficulty and distractors analysis

Additional Knowledge:
• Reliability: Refers to consistency of measurement across time, raters, or items (test-retest, inter-rater, internal consistency)
• Validity: Refers to whether a test measures what it purports to measure (content, criterion, construct validity)