Polytomous Rasch Models
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Polytomous Rasch Models book
The Rasch model presented in the last chapter is suitable for items scored as right or wrong, such as multiple-choice and true-false questions. It is not suitable for polytomous scored items, such as Likert scales. Masters’s (1982) partial credit model and Andrich’s (1978) rating scale model are two extensions of the Rasch model that are appropriate for polytomous items. Choosing a polytomous item response model depends on the testing context and procedures for item scoring. In educational settings, students may be awarded points that represent different degrees of correctness. For example, students taking a math test may be given no points for a completely incorrect answer, partial credit (1 point) for correctly answering part of the problem, and full credit (2 points) for correctly solving the whole problem. Students may also complete tasks that award credit for particular characteristics of a response. For example, students may be asked to write a short essay that is scored in one of five possible score levels (e.g. 0, 1, 2, 3, 4) that represent progressively more sophisticated qualities of creative writing.