In operational testing programs using item response theory (IRT), item parameter invariance is threatened when an item appears in a different location on the live test than it did when it was field tested. This study utilizes data from a large state's assessments to model change in Rasch item difficulty (RID) as a function of item position change,…

A number of vertical scaling methodologies were examined in this article. Scaling variations included data collection design, scaling method, item response theory (IRT) scoring procedure, and proficiency estimation method. Vertical scales were developed for Grade 3 through Grade 8 for 4 content areas and 9 simulated datasets. A total of 11 scaling…

Computer simulation indicated that reliability increased with the degree of similarity between underlying and observed distributions when the observed categorical distribution was deliberately constructed to match the shape of the underlying distribution of the trait being measured. Reliability also increased with correlation among variables and…

Type I error rates and rejection rates for three-dimensionality assessment procedures were studied with data sets simulated to reflect short tests and small samples. Results show that the G-squared difference test (D. Bock, R. Gibbons, and E. Muraki, 1988) suffered from a severely inflated Type I error rate at all conditions simulated. (SLD)

Many credentialing agencies today are either administering their examinations by computer or are likely to be doing so in the coming years. Unfortunately, although several promising computer-based test designs are available, little is known about how well they function in examination settings. The goal of this study was to compare fixed-length…

Examined the degree to which coefficient alpha is affected by including items with different distribution shapes within a unidimensional scale. Computer simulation results indicate that reliability does not increase dramatically as a result of using differentially shaped items within a scale. Discusses implications for test construction. (SLD)

This study compared vertical scaling results for the Rasch model from BILOG-MG and WINSTEPS. The item and ability parameters for the simulated vocabulary tests were scaled across 11 grades; kindergarten through 10th. Data were based on real data and were simulated under normal and skewed distribution assumptions. WINSTEPS and BILOG-MG were each…

Performed a simulation study to demonstrate the dramatic impact of capitalization on estimation errors on ability estimation in adaptive testing. Discusses four different strategies to minimize the likelihood of capitalization in computerized adaptive testing. (SLD)

Examined whether the item response theory (IRT) true-score equating method is more adversely affected by the presence of multidimensionality than two conventional equating methods, linear and equipercentile equating. Results of two simulation studies suggest that the IRT method performs as well as the conventional methods when the correlation…

Developed a new classification method for the logistic regression (LR) procedure for differential item functioning (DIF) based on methods used in the Simultaneous Item Bias test and conducted a simulation study to determine if the effect size measure affects the Type I error and power rates for the LR DIF procedure. Results show that inclusion of…

Conducted a simulation study of differential item functioning (DIF) to compare the power and Type I error rates for two conditions: using an examinee's ability estimate as the conditioning variable with the CATSIB program and either using the regression correction from CATSIB or not. Discusses implications of findings for DIF detection. (SLD)

Through a large-scale simulation study, this article compares item parameter estimates obtained by the marginal maximum likelihood estimation (MMLE) and marginal Bayes modal estimation (MBME) procedures in the 3-parameter logistic model. The impact of different prior specifications on the MBME estimates is also investigated using carefully…

Differential item functioning (DIF) analyses are used to identify items that operate differently between two groups, after controlling for ability. The Simultaneous Item Bias Test (SIBTEST) is a popular DIF detection method that matches examinees on a true score estimate of ability. However in some testing situations, like test translation and…

Recently, nonparametric methods have been proposed that provide a dimensionally based description of test structure for tests with dichotomous items. Because such methods are based on different notions of dimensionality than are assumed when using a psychometric model, it remains unclear whether these procedures might lead to a different…

This simulation investigated two procedures that reduce differences between paper-and-pencil testing and computerized adaptive testing (CAT) by making CAT content sensitive. Results indicate that the price in terms of additional test items of using constrained CAT for content balancing is much smaller than that of using testlets. (SLD)