The primary purpose of this study was to investigate the invariance properties of the Rasch model using data from standardized achievement tests that were not constructed to conform to the Rasch model. The item responses of approximately '3,400 examinees (Grades 9, 10, 11, and 12) to four separately timed sections of the Iowa Tests of Educational Development were analyzed. The results indicated that the Rasch model does yield reasonably invariant item parameter and ability parameter estimates for different tests and different examinee groups, even though the assumptions of the model are not met.As noted by many measurement experts, the use of latent trait models may help solve some of the measurement problems frequently encountered by practitioners (e.g., linking and equating of tests and building item banks). However, these models usually require rather strong assumptions about the nature of the data. The major assumption of all latent trait models is unidimensionality or, equivalently, local independence of items. Additional assumptions are required for each specific latent trait model. For dichotomously scored items, the oneparameter logistic, or Rasch, model, is the simplest latent trait model and consequently makes the most restrictive assumptions.
This paper examines the effects of test item disclosure on resulting examinee equated scores and population passing rates. The equating model studied was the common-item nonequivalent-populations design under Tucker linear equating procedures. The research involved simulating disclosure by placing correct answers of "disclosed" items into response vectors of selected examinees. The degree of exposure the disclosed items received in the population was manipulated by varying the number of items disclosed and the number of examinee records receiving the correct answers. Other factors considered among the 10 experimental conditions included the characteristics of the disclosed items (difficulty of disclosed items and whether they were anchor or nonanchor test items) and the ability level of the subgroup receiving the disclosed items. Results suggest that effects of disclosure depend on the nature of the released items. Specific effects of disclosure on particular examinees are also discussed. Index terms: equated scores, licensing exams, passing rates, simulated disclosure, test disclosure. The issue of test disclosure has become the focus of the debate surrounding truth-in-testing legislation. Between 1977 and 1983, approximately 90 testing bills were introduced in 28 states; five bills were introduced in the U.S. House of Representatives (Greer, 1984a). Although only two states-California and New York-have enacted truth-in
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