KR-20 is a measure of what property of a test?

• A. Validity
• B. Internal consistency reliability for dichotomous items
• C. Test-retest reliability
• D. Inter-rater reliability

Answer: (B)

KR-20 measures internal consistency reliability for tests with dichotomous items (scored right/wrong). It asks whether the items hang together as a coherent set that consistently reflects the same underlying construct. When students who do well on one item tend to do well on others, the items are considered to be measuring the same trait, and KR-20 rises toward 1. If items vary in what they tap or don’t relate well to each other, KR-20 drops.

This is a reliability index focused on item coherence among binary items, and it’s essentially a specialized form of Cronbach’s alpha for dichotomous data. It does not assess validity (whether the test measures what it should), it does not indicate stability over time (that would be test-retest reliability), and it does not reflect agreement between different raters (that’s inter-rater reliability).