If a test has low reliability, what is the impact on interpretation of norms?

• A. It improves cross-population applicability.
• B. It has no effect on interpretation.
• C. It undermines the validity of comparisons.
• D. It increases measurement error.

Answer: (C)

Reliability is about how consistently a test measures what it aims to measure. When a test has low reliability, a lot of the observed score comes from random error rather than true ability. Norms are meaningful only if scores reflect real differences among people; with a lot of error, a person’s position in the normative distribution can shift from one occasion to another just by chance. That makes comparisons to the normative group unstable and invalid, so interpreting where someone stands relative to the norms is undermined. In short, low reliability erodes the trustworthiness of norm-based interpretations because the scores aren’t stable reflections of true ability.