Glossary category
Measurement Quality
How researchers evaluate whether an assessment produces consistent scores and supports useful interpretations.
Construct Validity
Construct validity is the body of evidence supporting the interpretation that an assessment score represents the intended psychological construct. Researchers examine item content, score structure, expected links with similar and different measures, response processes, and competing explanations. It is built through multiple studies rather than established by one statistic.
Cronbach's Alpha
Cronbach's alpha is a coefficient commonly used to summarize the internal consistency of a multi-item score. It is influenced by item relationships, the number of items, and model assumptions. A high alpha can support a consistency argument, but it does not prove that items measure one construct, cover it well, remain stable over time, or yield valid interpretations.
Internal Consistency
Internal consistency describes how responses to items contributing to the same score relate to one another. It helps evaluate whether items behave as a coherent set, and is often summarized with coefficients such as Cronbach's alpha or omega. It does not show that a test is unidimensional, stable over time, or valid for its intended use.
Test Reliability
Test reliability is the consistency or precision of scores under specified conditions. A reliable assessment produces sufficiently similar results when the measured characteristic should be stable, or shows coherent evidence across relevant items. Reliability limits how confidently small score differences can be interpreted, but high reliability alone does not prove that the right construct is being measured.
Test Validity
Test validity is the degree to which evidence and theory support a particular interpretation and use of assessment scores. It is not a simple stamp that a test either has or lacks. Validity depends on what the score is claimed to mean, who takes the assessment, how it is administered, and what decisions follow from it.
Test-Retest Reliability
Test-retest reliability measures how consistently an assessment ranks or scores people across two or more occasions when the underlying characteristic is expected to remain reasonably stable. It is commonly estimated with a correlation or agreement statistic. The result depends on the time interval, population, testing conditions, and whether real change is plausible.
Validity vs Reliability
Reliability asks whether assessment scores are consistent or precise; validity asks whether evidence supports the meaning and use assigned to those scores. A measure can be reliable but invalid, because it may consistently measure the wrong thing. Valid interpretations usually require adequate reliability, but reliability by itself is never enough.