Abstract
This study compared several IRT calibration proce dures to determine which procedure, if any, consis tently produced the most accurate item parameter esti mates. A new criterion of calibration efficiency was used for evaluating the calibration procedures; this cri terion considers the joint effects of individual item pa rameter errors as they relate to the accuracy of θ esti mation. Four methods of item calibration were evaluated: (1) heuristic estimates obtained from trans formations of traditional item statistics; (2) ANCILLES, a program that first fits the c parameter and then trans forms traditional item statistics to IRT a and b parame ters ; (3) LOGIST, a joint maximum likelihood proce dure ; and (4) ASCAL, a modification of LOGIST'S algorithm which applies Bayesian priors to the abilities and item parameters. These were compared with each other and with a constant item parameter baseline con dition. ASCAL and LOGIST produced estimates of essen tially equivalent accuracy, although ASCAL's estimates of the c parameters were slightly superior. The heuris tic estimates and those from ANCILLES were generally poor in comparison, particularly for smaller sample sizes. Index terms: Calibration efficiency, Item calibration, Item parameter estimation, Item response theory, Latent trait models.
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