Browsing by Author "Vale, C. David"

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    Evaluation of the efficiency of item calibration
    (1988) Vale, C. David; Gialluca, Kathleen A.
    This study compared several IRT calibration procedures to determine which procedure, if any, consistently produced the most accurate item parameter estimates. A new criterion of calibration efficiency was used for evaluating the calibration procedures; this criterion considers the joint effects of individual item parameter errors as they relate to the accuracy of &thetas; estimation. Four methods of item calibration were evaluated: (1) heuristic estimates obtained from transformations of traditional item statistics; (2) ANCILLES, a program that first fits the c parameter and then transforms traditional item statistics to IRT a and b parameters ; (3) LOGIST, a joint maximum likelihood procedure ; 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 condition. ASCAL and LOGIST produced estimates of essentially equivalent accuracy, although ASCAL’s estimates of the c parameters were slightly superior. The heuristic 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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    Linking item parameters onto a common scale
    (1986) Vale, C. David
    An item bank typically contains items from several tests that have been calibrated by administering them to different groups of examinees. The parameters of the items must be linked onto a common scale. A linking technique consists of an anchoring design and a transformation method. Four basic anchoring designs are the unanchored, anchor-items, anchor-group, and double-anchor designs. The transformation design consists of the system of equations that is used to translate the anchor information and put the item parameters on a common scale. Several transformation methods are discussed briefly. A simulation study is presented that compared the equivalent-groups method with the anchor-items method, using varying numbers of common items, applied both to the situation in which the groups were equivalent and one in which they were not. The results confirm previous findings that the equivalent-groups method is adequate when the groups are in fact equivalent. When the groups are not equivalent, accurate linking can be obtained with as few as two common items. Linking using a more efficient interlaced anchor-items design can provide accurate linking without the expense of including explicit common items in each of the tests.