What is the difference between reliability and validity in assessment?

• A. Reliability is about bias.
• B. Reliability refers to test length.
• C. Reliability is the consistency of scores across time and forms.
• D. Validity is the extent to which a test measures what it intends to measure.

Answer: (C)

Reliability asks whether scores stay consistent across time and across different versions of the test. If a student takes the same test again on another day, or if a different but equivalent form of the test is used, the scores should be similar if the student’s true ability hasn’t changed. That stable, repeatable nature is what we mean by reliability, and the option that describes consistency across time and forms captures this idea precisely.

Validity, in contrast, is about meaning: does the test actually measure what it intends to measure, and do the inferences we make from the scores reflect the real skills or knowledge of interest? A test can be reliably consistent yet fail to measure the intended construct, which is why validity and reliability are related but distinct concepts.

The other statements don’t define reliability: bias concerns fairness and how well the test targets the intended construct (a validity issue), and test length doesn’t define reliability.