Psychometrics: Trust, but Verify

There is a continued mandate for practicing evidence-based medicine and the prerequisite rigorous analysis of the comparative effectiveness of alternative treatments. There is also an increasing emphasis on delivering value-based health care. Both these high priorities and their related endeavors require correct information about the outcomes of care. Accurately measuring and confirming health care outcomes are thus likely now of even greater importance. The present basic statistical tutorial focuses on the germane topic of psychometrics. In its narrower sense, psychometrics is the science of evaluating the attributes of such psychological tests. However, in its broader sense, psychometrics is concerned with the objective measurement of the skills, knowledge, and abilities, as well as the subjective measurement of the interests, values, and attitudes of individuals-both patients and their clinicians. While psychometrics is principally the domain and content expertise of psychiatry, psychology, and social work, it is also very pertinent to patient care, education, and research in anesthesiology, perioperative medicine, critical care, and pain medicine. A key step in selecting an existing or creating a new health-related assessment tool, scale, or survey is confirming or establishing the usefulness of the existing or new measure; this process conventionally involves assessing its reliability and its validity. Assessing reliability involves demonstrating that the measurement instrument generates consistent and hence reproducible results-in other words, whether the instrument produces the same results each time it is used in the same setting, with the same type of subjects. This includes interrater reliability, intrarater reliability, test-retest reliability, and internal reliability. Assessing validity is answering whether the instrument is actually measuring what it is intended to measure. This includes content validity, criterion validity, and construct validity. In evaluating a reported set of research data and its analyses, in a similar manner, it is important to assess the overall internal validity of the attendant study design and the external validity (generalizability) of its findings.