Reliability vs validity in psychological testing. Which statement best differentiates the two concepts?

• A. Reliability measures accuracy of a test, while validity measures consistency.
• B. Reliability is the extent to which a test measures what it is intended to measure.
• C. Reliability is the consistency of a measure across time or items; validity is the extent to which the test measures what it is intended to measure.
• D. Reliability and validity are identical concepts.

Answer: (C)

Reliability is about consistency: a test should give stable results across time or across its items. Validity is about accuracy: a test should measure the construct it is intended to measure. The statement that reliability is the consistency of a measure across time or items and validity is the extent to which the test measures what it is intended to measure captures the essential difference. Remember, a test can be reliable but not valid if it yields consistent results that don’t reflect the intended trait, while validity depends on reliability to exist in the first place.