What does it mean if a test is highly reliable but not valid?

A test that is highly reliable but not valid indicates that it consistently yields the same results each time it is administered, which reflects its reliability. However, this consistency does not guarantee that the test is measuring what it is intended to measure, known as validity. Therefore, when a test is reliable but not valid, it means that while you can expect to obtain the same score repeatedly under the same conditions, those scores may not accurately reflect the true traits or abilities that the test aims to assess.

In the context of measuring psychological constructs, this scenario can arise if, for example, a test designed to measure intelligence consistently produces the same score for an individual but is in fact assessing unrelated factors, such as test-taking strategies or anxiety levels. As a result, you can trust that the scores are dependable, but that dependability is misplaced if the scores do not represent the actual intelligence of the individual.

This understanding is crucial for practitioners who rely on test scores for decisions, as it highlights the importance of both reliability and validity in test construction and interpretation.