Which statement expresses the idea that a measurement can be reliable but not valid?

• A. A measure is always reliable and valid
• B. A measure cannot be reliable
• C. A measure can be reliable but not valid
• D. Validity always accompanies reliability

Answer: (C)

Reliability means the measurement yields consistent results across trials or raters. Validity means the results truly reflect the intended attribute or construct. A measurement can be reliable but not valid when it gives the same results repeatedly, yet those results do not represent what you actually want to measure. For example, a scale that is consistently 5 pounds off is reliable (it repeats the same error) but not valid for measuring true body weight. Because reliability shows consistency, but validity requires accuracy for the intended purpose, you can have one without the other. That’s why the statement that a measure can be reliable but not valid is the best way to express this idea.