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Abstract
The partial credit model, which is a special case of the Rasch measurement model, was presented as a useful way to develop and refine complex nursing assessments. The advantages of the Rasch model over the classical psychometric model were presented including the lack of bias in the measurement process, the ability to highlight those items in need of refinement, the provision of information on congruence between the data and the model, and feedback on the usefulness of the response categories. The partial credit model was introduced as a way to develop complex nursing assessments such as performance-based assessments, because of the model's ability to accommodate a variety of scoring procedures. Finally, an application of the partial credit model was illustrated using the Practical Knowledge Inventory for Nurses, a paper-and-pencil instrument that measures on-the-job decision-making for nurses.
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The partial credit model (Masters, 1982) is a special case of the Rasch measurement model that is used in test construction and calibration. The Rasch model overcomes several problems with traditional measurement models and has been used to advance test development practices in numerous disciplines. Because of its flexibility in item format, the partial credit model is one type of Rasch model that is particularly advantageous in the development and refinement of complex nursing assessments. Thus, the focus of this article is to highlight the features of the partial credit model and its application to nursing assessments.
An introduction to Rasch model will be presented first followed by a presentation of the partial credit model. Comparisons to traditional psychometric theory will be presented to emphasize the advantages of the Rasch model. This discussion will be extended to the partial credit model where applications to complex nursing assessments such as performance-based assessments, will be presented. Finally, the Practical Knowledge Inventory for Nurses (Fox, 1994) will be used to illustrate the features of the partial credit model.
The Rasch Model
Most tests are developed, scored, and interpreted based on classical psychometric theory. However, classical psychometric theory is only one of three primary measurement models (Snyder & Sheehan, 1992). The other two models are item response theory and generalizability theory. The Rasch model (Rasch, 1961, 1980) belongs to the former of these two.
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