Levels-based mark schemes and marking bias

Reliability and validity are ever-present themes in the evaluation of assessment. Previous research studies have considered the role of the question paper, the mark scheme and the examiners in providing unbiased estimates of students’ ability. With particular reference to the mark scheme, this paper focuses on how the rules imposed by levels-based mark schemes might affect the extent to which a measurement can be considered unbiased. It considers neither cognitive strategies nor the role of judgement instead, from a purely statistical point of view, it investigates the potential impact of mark scheme design. It concludes that the responses to a question itself should shape the mark distribution, rather than the shape being determined by the structure of the mark scheme. To this end, and pending further research in the area, it recommends that levels-based mark schemes should be designed such that each band is of equal width.

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