Mixture IRT models address the heterogeneity in a population by extracting latent classes and allowing item parameters to vary between latent classes. Once the latent classes are extracted, they need to be further examined to be characterized. Some approaches have been adopted in the literature for this purpose. These approaches examine either the…

This study is an examination of the incremental validity of Cattell-Horn-Carroll (CHC) broad clusters from the Woodcock-Johnson III Tests of Cognitive Abilities (WJ III COG) for predicting scores on the Woodcock-Johnson III Tests of Achievement (WJ III ACH). The participants were children and adolescents, ages 6-18 (n = 4,722), drawn from the WJ…

Background: Subtest and factor scores have typically provided little incremental predictive validity beyond the omnibus IQ score. Aims: This study examined the incremental validity of Wechsler Intelligence Scale for Children-Fourth UK Edition (WISC-IV[superscript UK]; Wechsler, 2004a, "Wechsler Intelligence Scale for Children-Fourth UK…

This addendum to previously published results presents alternative analyses of data from large-scale effectiveness studies of Cognitive Tutor Algebra I in middle schools and high schools. These alternative analyses produce results that are substantively the same as previously reported. We find a significant positive effect of 0.21 standard…

This cross-sectional descriptive study of the Model of Domain Learning, which describes learners' progress from acclimation through competence to proficiency through the interplay of knowledge, interest and strategic processing/critical thinking (CT), examined its extension to maternity nursing. Based on the identified need for valid, reliable…

This tutorial summarizes some of the widely known limitations of tests of statistical significance and then focuses on extracting measures of variation accounted for as a supplement to significance testing. Two measures of variation accounted for, eta squared and omega squared, are discussed. Computational formulas, computational examples, and…

The development and evaluation of methods for detecting potentially biased items or differentially functioning items (DIF) represent a critical area of research for psychometricians because of the negative impact of biased items on test validity. A summary is provided of the authors' 12 years of research at the University of Massachusetts…