Congeneric and (Essentially) Tau-Equivalent Estimates of Score Reliability: What They Are and How to Use Them

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 measu...

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Bibliographic Details
Published in:Educational and psychological measurement 2006-12, Vol.66 (6), p.930-944
Main Author: Graham, James M.
Format: Article
Language:English
Subjects:
Biological and medical sciences
Error of Measurement
Fundamental and applied biological sciences. Psychology
Goodness of Fit
Heuristics
Internal Consistency
Mathematical Models
Psychology. Psychoanalysis. Psychiatry
Psychology. Psychophysiology
Psychometrics
Psychometrics. Statistics. Methodology
Reliability
Researchers
Scores
Statistics. Mathematics
Structural Equation Models
Test Items
Test Theory
Citations: Items that this one cites
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Summary: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.
ISSN:0013-1644
1552-3888
DOI:10.1177/0013164406288165