Difficulty and discrimination indices as quality assurance tools for assessments in a South African problem-based pharmacy programme

This study investigated the difficulty and discrimination ability of examination questions in an undergraduate pharmacy programme presented at the Medunsa Campus of the University of Limpopo, South Africa. This investigation was part of an education study, which evaluated the quality of knowledge assessments in this outcomes and problem-based BPharm programme. Indices of difficulty (where a higher index characterises an easier item) and indices of discrimination were calculated for each True/False item and constructed response question from a total of 15 summative examinations in the first- to fourth-year level. We adapted the item analysis calculation methods to additionally accommodate questions counting more than one mark. Mean difficulty indices were 66.7% for True/False items without negative marking; 55.1% with negative marking, and 60.1% for constructed response questions. Discrimination indices for True/False items were 0.22 without negative marking, 0.24 with negative marking, and 0.28 for constructed response questions. Factors are discussed which potentially influence the difficulty and discrimination of examination items and the usefulness of item analysis techniques to review and improve future assessments in this programme.