Which statement about reliability and validity is true?

• A. Reliability and validity are interchangeable; either one guarantees trustworthiness.
• B. A measure cannot be reliable and invalid at the same time.
• C. It is possible for a measure to be reliable but not valid.
• D. Validity guarantees reliability.

Answer: (C)

Reliability means the measurement yields consistent results across repeated tests or different raters, while validity means the instrument actually measures the intended construct. It's possible for a tool to be consistently off-target yet still give the same readings each time—that would be reliable but not valid. For example, a scale that is always 2 kilograms too high will produce repeatable numbers, but those numbers don’t reflect true weight, so the measure is reliable but invalid. Conversely, validity implies the measurement is appropriate for what you’re trying to assess, but that alone doesn’t guarantee that it will be perfectly consistent across trials or raters. In short, a measure can be reliable without being valid, so the true statement is that reliability and validity are related but distinct, and reliability does not automatically ensure validity.