Coefficient alpha and the internal structure of tests
 Lee J. Cronbach
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A general formula (α) of which a special case is the KuderRichardson coefficient of equivalence is shown to be the mean of all splithalf coefficients resulting from different splittings of a test. α is therefore an estimate of the correlation between two random samples of items from a universe of items like those in the test. α is found to be an appropriate index of equivalence and, except for very short tests, of the firstfactor concentration in the test. Tests divisible into distinct subtests should be so divided before using the formula. The index \(\bar r_{ij} \) , derived from α, is shown to be an index of interitem homogeneity. Comparison is made to the Guttman and Loevinger approaches. Parallel split coefficients are shown to be unnecessary for tests of common types. In designing tests, maximum interpretability of scores is obtained by increasing the firstfactor concentration in any separatelyscored subtest and avoiding substantial groupfactor clusters within a subtest. Scalability is not a requisite.
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 Title
 Coefficient alpha and the internal structure of tests
 Journal

Psychometrika
Volume 16, Issue 3 , pp 297334
 Cover Date
 19510901
 DOI
 10.1007/BF02310555
 Print ISSN
 00333123
 Online ISSN
 18600980
 Publisher
 SpringerVerlag
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 Authors

 Lee J. Cronbach ^{(1)}
 Author Affiliations

 1. University of Illinois, USA