Estimation of Internal Consistency Reliability When Test Parts Vary in Effective Length

Evaluating a test's reliability often requires dividing it into 3 or more unequal parts, which causes violation of the tau equivalence assumption of Cronbach's alpha. This article presents a criterion for abandoning alpha and an approach for computing a more appropriate estimate of reliability, the Gilmer-Feldt coefficient (J. S. Gilmer & L. S. Feldt, 1983).