Placing candidates who take differentiated papers on a common grade scale

Three methods of transferring marks from differentiated papers examinations on to a common grade scale are compared. Equipercentile scaling and linear scaling prior to grading gave very similar grades; but grading the different versions of the examination separately, without scaling the component marks for difficulty, resulted in the award of different grades to a substantial proportion of the candidates. The advantages and shortcomings of each method are considered and also whether a scaling method or separate grading is to be preferred. It is concluded that a scaling method should be used, and that the grades from linear scaling are likely to be the most satisfactory.

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