KR-21 reliability and its extension (coefficient [alpha]) gives the reliability estimate of test scores under the assumption of tau-equivalent forms. KR-21 reliability gives the reliability estimate for summed scores for dichotomous items when items are randomly sampled from an infinite pool of similar items (randomly parallel forms). The article…

A method for medical screening is adapted to differential item functioning (DIF). Its essential elements are explicit declarations of the level of DIF that is acceptable and of the loss function that quantifies the consequences of the two kinds of inappropriate classification of an item. Instead of a single level and a single function, sets of…

The proposed coefficient is derived by assuming that the average Goodman-Kruskal gamma between items of identical difficulty would be the same for items of different difficulty. An estimate of covariance between items of identical difficulty leads to an estimate of the correlation between two tests with identical distributions of difficulty.…

An important relationship is given for two generalizations of coefficient alpha: (1) Rajaratnam, Cronbach, and Gleser's generalizability formula for stratified-parallel tests, and (2) Raju's coefficient beta. (Author/CTM)

A major deficiency in classical test theory is the reliance on Pearson product-moment (PPM) correlation concepts in the definition of reliability. PPM measures are totally insensitive to first moment differences in tests which leads to the dubious assumption of essential tan-equivalence. Robinson proposed a measure of agreement that is sensitive…

Different indices for the internal consistency, reproducibility, or homogeneity of a test are based upon highly similar conceptual frameworks. Illustrations are presented to demonstrate how the maximum and minimum values of KR20 are influenced by test difficulty and the shape of the distribution of test scores. (Author/CTM)

The binomial error model includes form-to-form difficulty differences as error variance and leads to Ruder-Richardson formula 21 as an estimate of reliability. If the form-to-form component is removed from the estimate of error variance, the binomial model leads to KR 20 as the reliability estimate. (Author/BW)

Undergraduates in five classes were asked to rate their instructors on four general items, and on twenty-four behavior-specific items describing instructor involvement. Three reliability coefficients differing in error score assumptions were calculated for different numbers of students and items, to permit comparison of the reliabilities of both…