The probabilistic character of relevance

Gebhardt's[1] probabilistic model of relevance is examined and found not to represent adequately some characteristics of the relevance judgement process. An alternative model is proposed, which identifies two different types of “error” or probabilistic variation between relevance judgements. The two types arise from, first, the definition of the boundaries of the relevance classes, and secondly the actual assessment of an individual document on the underlying scale (which is assumed to be a continuum). The problems of quantifying the model, and of assessing its implications for retrieval testing, are discussed.