DIMTEST is a nonparametric statistical test procedure for assessing unidimensionality of binary item response data that uses the T-statistic of W. F. Stout (1987). This study investigates the performance of the T-statistic with respect to different shapes of ability distributions and confirms its nonparametric nature. (SLD)

A modification of the SIBTEST procedure to assess differential item functioning (DIF) for two-dimensional test data (i.e., data for tests where two intended abilities are tapped by test items) is described. A small simulation study is carried out to assess the performance of the modified SIBTEST to detect DIF in such two-dimensional data. The…

In many large-scale educational assessments it is of interest to compare the distribution of latent abilities of different subpopulations, and track these distributions over time to monitor educational progress. B. Junker, together with two colleagues, has developed a simple scheme, based on the proportion correct score, for smoothly approximating…

The capability of the DIMTEST statistical test to assess essential dimensionality of the model underlying item responses of real tests as opposed to simulated tests was investigated. A variety of real test data from difference sources was used to assess essential dimensionality. Based on DIMTEST results, some test data are assessed as fitting an…

A statistical method, W. F. Stout's statistical test of essential unidimensionality (1990), for exploring the lack of unidimensionality in test data was studied using Monte Carlo simulations. The statistical procedure is a hypothesis test of whether the essential dimensionality is one or exceeds one, regardless of the traditional dimensionality.…

Computerized adaptive tests (CATs) pose major obstacles to the traditional assessment of differential item functioning (DIF). This paper proposes a modification of the SIBTEST DIF procedure for CATs, called CATSIB. CATSIB matches test takers on estimated ability based on unidimensional item response theory. To control for impact-induced Type I…

Using simulated and real data, this study compares the performance of three methodologies for assessing unidimensionality: (1) DIMTEST; (2) the approach of Holland and Rosenbaum; and (3) nonlinear factor analysis. All three models correctly confirm unidimensionality, but they differ in their ability to detect the lack of unidimensionality.…

By definition, differential item functioning (DIF) refers to unequal probabilities of a correct response to a test item by examinees from two groups when controlled for their ability differences. Simulation results are presented for an attempt to purify a test by separating out multidimensional items under the assumption that the intent of the…

The performance of the following four methodologies for assessing unidimensionality was examined: (1) DIMTEST; (2) the approach of P. W. Holland and P. R. Rosenbaum; (3) linear factor analysis; and (4) non-linear factor analysis. Each method is examined and compared with other methods using simulated data sets and real data sets. Seven data sets,…

DIMTEST is a statistical test procedure for assessing essential unidimensionality of binary test item responses. The test statistic T used for testing the null hypothesis of essential unidimensionality is a nonparametric statistic. That is, there is no particular parametric distribution assumed for the underlying ability distribution or for the…