Are Secondary Assessors Uncertain When They Disagree About Relevance Judgements?

The collection of relevance judgements by assessors is important for many information retrieval (IR) tasks. In addition to the construction of test collections, relevance judging is critical to e-discovery and other applications where many assessors are hired to perform relevance judging. It is well known that assessors may differ in their judgements for a given document. One possible cause of a judgement difference is that an assessor may be uncertain in their judgement and thus may in effect be guessing the document's relevance. If assessors are aware of their uncertainty and can self-report their level of certainty, then uncertain relevance judgements can be targeted for adjudication by additional assessors. In this paper, we conducted a user study with 48 participants to test our hypothesis that assessors will be uncertain about their relevance judgements when the assessors are likely to disagree with each other. We found that for low consensus documents, i.e. documents known for assessor disagreement, assessors judge these documents with almost as much certainty as high consensus documents. In particular, assessor self-reported uncertainty is predictive of disagreement only for high consensus documents and not for low consensus documents.