Results of this simulated study indicate that, when unidimensional stimulus sets are scaled in two dimensions using a rational starting configuration, the nature of the two-dimensional configuration can indicate the general form of the function mapping psychological dissimilarity--represented as distance in the scaling model--onto the observed…

Three multitrait-multimethod studies are described, which indicated that ill-defined solutions were frequent, and alternative parameterizations tended only to mask this problem. Moreover, method factors sometimes represented trait variance as opposed to method variance. However, specification of method effects as correlated uniqueness proved more…

The fundamental mathematical model of L. L. Thurstone's common factor analysis is reviewed, and basic covariance matrices of maximum likelihood factor analysis and alpha factor analysis are presented. The methods are compared in terms of computational and scaling contrasts. Weighting and the appropriate number of common factors are considered.…

Simulation studies (N=4,000 simulees) examined the effect of misspecification of the latent ability distribution (theta) on the accuracy and efficiency of marginal maximum likelihood (MML) item parameter estimates and on MML statistics to test sufficiency and conditional independence. Results were compared to those of the conditional maximum…

The standard error (SE) of correlations adjusted for selection with commonly used formulas was investigated. The study provides large-sample approximations of SE using the Pearson-Lawley three-variable correction formula, examines the SE under specific conditions, and compares various estimates of SEs under direct and indirect selection. (TJH)

The Multidimensional Personality Questionnaire (MPQ) was parameterized using the 2-parameter logistic item response (IRT) model. Two samples of 1,000 adults were used. Results suggest that the 2-parameter model fits the MPQ data, and researchers assessing normal-range personality processes have much to gain from exploiting IRT models. (TJH)

This study examined the application of the marginal maximum likelihood-EM algorithm to the parameter estimation problems of the normal ogive and logistic polytomous response models for Likert-type items. A rating scale model, based on F. Samejima's (1969) graded response model, was developed. (TJH)

The effects of priors and amount of bias in the Bayesian approach to the estimation problem in item response models are examined using simulation studies. Different specifications of prior information have only modest effects on Bayesian estimates, which are less biased than joint maximum likelihood estimates for small samples. (TJH)

Geometric approaches to representing interrelations among tests and items are compared with an additive tree model (ATM), using 2,644 examinees and 2 other data sets. The ATM's close fit to the data and its coherence of presentation indicate that it is the best means of representing tests and items. (TJH)

In this study, 590 third graders from 12 Dutch schools took 32 tests indicating 16 semantic Structure-of-Intellect (SI) abilities and 1 of 4 reading comprehension tests, involving either multiple-choice or open-ended items. Results indicate that item type for reading comprehension is congeneric with respect to SI abilities measured. (TJH)