Understanding the error of our ways: Mapping the concepts of validity and reliability

Clinicians increasingly desire evidence upon which to base their practice decisions. One of the difficulties in their decision-making, however, is answering the fundamental question, "How do I evaluate the relevance and applicability of the findings?" There are a number of factors involved in such an evaluation and, frequently, readers can easily determine the usefulness of a study's findings based on similarities to their own clinical setting, timeframe, and/or patient population. It may be more difficult, however, to understand and evaluate a study's measurement error, or the reliability (trustworthiness) and validity (truth) of its methods and measurement strategies, in part because the extensive body of literature associated with validity and reliability can be overwhelming. The purpose of this article is to provide a comprehensive overview of measurement error as it applies to research design and instrumentation issues. It is intended to serve as a succinct, practical reminder of the definitions and relationships of the concepts of validity and reliability. It is not intended to replace the essential, detailed discussions found in numerous textbooks and journal articles. The different dimensions of validity and reliability are briefly discussed and a concept map is used to illustrate their relationships. In the process of explaining or predicting the phenomena and/or processes of health care, researchers and clinicians must be able to evaluate the truthfulness, precision, and dependability of the instruments and measurement methods used to generate the knowledge for evidence-based practice.