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ERIC Number: ED421535
Record Type: Non-Journal
Publication Date: 1997-Jun
Pages: 64
Abstractor: N/A
Reference Count: N/A
Evaluation of Parameter Estimation under Modified IRT Models and Small Samples.
Parshall, Cynthia G.; Kromrey, Jeffrey D.; Chason, Walter M.; Yi, Qing
Accuracy of item parameter estimates is a critical concern for any application of item response theory (IRT). However, the necessary sample sizes are often difficult to obtain in practice, particularly for the more complex models. A promising avenue of research concerns modified item response models. This study both replicates and improves on an earlier investigation into modified models (C. Parshall, J. Kromrey, and W. Chason, 1996), which found tentatively positive results. To obtain realistic data, empirical item parameters were generated by fitting a six-dimensional model to archival data, using NOHARM (Fraser and McDonald, 1988). These parameters were then used along with thetas generated from independent normal ability distributions to generate simulated item response data. One hundred datasets were generated for each of four sample sizes. Finally, BILOG (Mislevy and Bock, 1990) was used to obtain estimated item ability parameters for each of the six investigated models. Results were evaluated in terms of accuracy and stability across samples. Accuracy was assessed as the degree to which both the obtained item responses and the known response probabilities were reproduced from the generating parameters. Stability was assessed as empirical estimates of standard errors. Crossvalidation of fit and accuracy was accomplished by applying the sample item parameter estimates to additional samples generated from the same population. (Contains 5 tables, 17 figures, and 27 references.) (Author)
Publication Type: Reports - Research; Speeches/Meeting Papers
Education Level: N/A
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A