Improving Pairwise Rank Aggregation via Querying for Rank Difference

Pairwise rank aggregation (PRA) aims at learning a ranking from pairwise comparisons between objects that specify their relative ordering. The present study proposes the use of rank difference information for PRA, which characterizes the extent winners in paired comparisons beat their opponents. While such information can be effortlessly recognized by annotators, to our knowledge, it has not been utilized for PRA before. The challenge is three-fold: how to solicit such information, how to utilize it in rank aggregation, and how to overcome the noise from heterogeneous annotators. This study proposes a new query for soliciting information about rank difference that imposes limited cognitive burden on annotators. As prior methods for PRA abounds, it is of interest to empower them with information on rank difference. To this end, this study proposes a conservative learning objective that can be combined seamlessly with many existing PRA algorithms. The third contribution is a new method for PRA called mixture of exponentials (MoE). Annotators from a heterogeneous population might have diverse views concerning rank difference. For example, an annotator might be good at recognizing rank difference only for a subset of items but not the rest. This means that information about rank difference is likely to be perturbed. Unfortunately, such an object-dependent error pattern cannot be modeled with existing approaches. MoE assumes that each annotator uses a mixture of ranking functions in generating answers, and the mixture components can capture object-related patterns in data. The present study evaluates the proposals with extensive experiments on both real and synthetic datasets. The results confirm the efficacy of the proposals and shed light on their practical usage.