ERIC Number: EJ745770
Record Type: Journal
Publication Date: 2006
Reference Count: 22
Congeneric and (Essentially) Tau-Equivalent Estimates of Score Reliability: What They Are and How to Use Them
Graham, James M.
Educational and Psychological Measurement, v66 n6 p930-944 2006
Coefficient alpha, the most commonly used estimate of internal consistency, is often considered a lower bound estimate of reliability, though the extent of its underestimation is not typically known. Many researchers are unaware that coefficient alpha is based on the essentially tau-equivalent measurement model. It is the violation of the assumptions required by this measurement model that are often responsible for coefficient alpha's underestimation of reliability. This article presents a hierarchy of measurement models that can be used to estimate reliability and illustrates a procedure by which structural equation modeling can be used to test the fit of these models to a set of data. Test and data characteristics that can influence the extent to which the assumption of tau-equivalence is violated are discussed. Both heuristic and applied examples are used to augment the discussion. (Contains 2 figures and 3 tables.)
Descriptors: Models, Test Theory, Reliability, Structural Equation Models, Goodness of Fit, Heuristics, Test Items, Error of Measurement, Scores, Researchers, Mathematical Models
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Publication Type: Journal Articles; Reports - Evaluative
Education Level: N/A
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