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Item banking for C-tests: A polytomous Rasch modeling approach

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Author(s): Thomas Eckes

Journal: Psychological Test and Assessment Modeling
ISSN 2190-0493

Volume: 53;
Issue: 4;
Start page: 414;
Date: 2011;
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Keywords: polytomous Rasch models | item banking | language testing | C-test | local item dependence

ABSTRACT
C-tests are gap-filling tests widely used to assess general language proficiency for purposes of placement, screening, or provision of feedback to language learners. C-tests consist of several short texts in which parts of words are missing. Development, administration, and scoring of C-tests are particularly efficient when use is made of a calibrated item bank. Rasch measurement provides a powerful approach to item bank construction. Based on construing C-test texts as superitems, where item values correspond to the number of gaps in the text filled in correctly, two polytomous Rasch models were applied to analyze and evaluate a large set of texts: Andrich’s (1978) rating scale model and Müller’s (1987, 1999b) continuous rating scale model. The test construction phase comprised a total of 218 texts trialled in 27 independent samples, covering a total of 5,927 participants. Across samples, reliability indices ranged from .94 to .98. Texts showing unsatisfactory model fit or DIF were eliminated. The remaining texts were put on the same difficulty scale through a concurrent estimation procedure. Results clearly attested to the suitability of polytomous Rasch models to calibrate texts for purposes of item banking.

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