Incentives for Item Duplication under Fair Ranking Policies

TL;DR

This paper investigates how fair ranking policies can incentivize item duplication, leading to increased redundancy and potential fairness issues, especially in systems where duplicates gain extra exposure.

Contribution

It is the first study to analyze the impact of fair ranking policies on incentivizing item duplication and its implications for fairness and diversity.

Findings

Fair ranking policies may incentivize duplication due to exposure benefits.

Duplicates can gain significantly more exposure under fairness-aware policies.

Incentivizing duplication conflicts with diversity and fairness objectives.

Abstract

Ranking is a fundamental operation in information access systems, to filter information and direct user attention towards items deemed most relevant to them. Due to position bias, items of similar relevance may receive significantly different exposure, raising fairness concerns for item providers and motivating recent research into fair ranking. While the area has progressed dramatically over recent years, no study to date has investigated the potential problem posed by duplicated items. Duplicates and near-duplicates are common in several domains, including marketplaces and document collections available to search engines. In this work, we study the behaviour of different fair ranking policies in the presence of duplicates, quantifying the extra-exposure gained by redundant items. We find that fairness-aware ranking policies may conflict with diversity, due to their potential to incentivize duplication more than policies solely focused on relevance. This fact poses a problem for system owners who, as a result of this incentive, may have to deal with increased redundancy, which is at odds with user satisfaction. Finally, we argue that this aspect represents a blind spot in the normative reasoning underlying common fair ranking metrics, as rewarding providers who duplicate their items with increased exposure seems unfair for the remaining providers.