Credit Model

Computerized adaptive testing prrcedures (CATPs) based on the graded response method (GRM) of F. Samejima (1969) and the partial credit model (PCM) of G. Masters (1982) were developed and compared. Both programs used maximum likelihood estimation of ability, and item selection was conducted on the basis of information. Two simulated data sets, one wi h 1,000 simulated examinees and one with 500 simulated examinees, were generated according to a linear analytic model. Both contained responses to 180 five-alternative items, of which 55 were retained for 997 simulated examinees with infit statistics between-3.0 and 3.0. The MULTILOG calibration program of D. J. Thissen (1988) was used to obtain item parameter estimates for both models from the data zet. It was expected that using a data set fitted to the PCM model would result in no differences between PCM and GRM CATPs. However, the GRM CATPs provided more accurate information than did the PCM CATPs and the estimation was considered adequate. Reasons for difficulties with the PCM model are discussed. Two tables and five graphs present study data. (SLD) * Reproductions supplied by EDRS are the best that can be made * * from the original dccument.