A robust approach for mapping group marks to individual marks using peer assessment

Group work can form a substantial component of degree programme assessments. To satisfy institutional and student expectations, students must often be assigned individual marks for their contributions to the group project, typically by mapping a single holistic group mark to individual marks using peer assessment scores. Since the early 1990s, various mapping methods that use self- and peer ratings have been developed. They are based on (normalised) individual weighting factors, partial scaling of the group mark, inter-rater agreement corrections or parabolic functions. We show that no single existing method can be successfully applied to most practical peer assessment scenarios such as different marking scale interpretations, intra-group ranking errors, biased free-riders and marks exceeding 100%. We present a combined analytical mapping method that incorporates the benefits of existing mechanisms, but alleviates their weaknesses with minimum computational effort and tutor input. The robustness of the me...