A kitchen scale that is not properly calibrated may consistently under- or overestimate the weight of cereal. Although the scale is highly reliable because it yields the same reading every time, the results are incorrect, illustrating that a measure can be reliable but invalid.

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A key distinction in research methodology is that a measure can be reliable, meaning it consistently produces the same result, without being valid, as it may not accurately measure the intended concept. Conversely, any measure that is considered valid must inherently be reliable. Therefore, while validity necessitates reliability, reliability alone does not guarantee validity.

Relationship Between Reliability and Validity

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

A measurement tool can yield highly consistent results without actually measuring the intended construct. For instance, attempting to measure a person's self-esteem by using a ruler to measure their index finger length would demonstrate excellent test-retest reliability, as finger length is stable over time. However, this method would have absolutely no validity, as finger length has no conceptual relationship to self-esteem.

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