We introduce the concept of expected exposure as the average attention ranked items receive from users over repeated samples of the same query. Furthermore, we advocate for the adoption of the principle of equal expected exposure: given a fixed information need, no item should receive more or less expected exposure than any other item of the same relevance grade. We argue that this principle is desirable for many retrieval objectives and scenarios, including topical diversity and fair ranking. Leveraging user models from existing retrieval metrics, we propose a general evaluation methodology based on expected exposure and draw connections to related metrics in information retrieval evaluation. Importantly, this methodology relaxes classic information retrieval assumptions, allowing a system, in response to a query, to produce a distribution over rankings instead of a single fixed ranking. We study the behavior of the expected exposure metric and stochastic rankers across a variety of information access conditions, including ad hoc retrieval and recommendation. We believe that measuring and optimizing expected exposure metrics using randomization opens a new area for retrieval algorithm development and progress. CCS CONCEPTS • Information systems → Evaluation of retrieval results; Learning to rank.

Ride hailing platforms, such as Uber, Lyft, Ola or DiDi, have traditionally focused on the satisfaction of the passengers, or on boosting successful business transactions. However, recent studies provide a multitude of reasons to worry about the drivers in the ride hailing ecosystem. The concerns range from bad working conditions and worker manipulation to discrimination against minorities. With the sharing economy ecosystem growing, more and more drivers financially depend on online platforms and their algorithms to secure a living. It is pertinent to ask what a fair distribution of income on such platforms is and what power and means the platform has in shaping these distributions.In this paper, we analyze job assignments of a major taxi company and observe that there is significant inequality in the driver income distribution. We propose a novel framework to think about fairness in the matching mechanisms of ride hailing platforms. Specifically, our notion of fairness relies on the idea that, spread over time, all drivers should receive benefits proportional to the amount of time they are active in the platform. We postulate that by not requiring every match to be fair, but rather distributing fairness over time, we can achieve better overall benefit for the drivers and the passengers. We experiment with various optimization problems and heuristics to explore the means of achieving two-sided fairness, and investigate their caveats and side-effects. Overall, our work takes the first step towards rethinking fairness in ride hailing platforms with an additional emphasis on the well-being of drivers.

Rankings of people and items are at the heart of selection-making, match-making, and recommender systems, ranging from employment sites to sharing economy platforms. As ranking positions influence the amount of attention the ranked subjects receive, biases in rankings can lead to unfair distribution of opportunities and resources such as jobs or income.This paper proposes new measures and mechanisms to quantify and mitigate unfairness from a bias inherent to all rankings, namely, the position bias which leads to disproportionately less attention being paid to low-ranked subjects. Our approach differs from recent fair ranking approaches in two important ways. First, existing works measure unfairness at the level of subject groups while our measures capture unfairness at the level of individual subjects, and as such subsume group unfairness. Second, as no single ranking can achieve individual attention fairness, we propose a novel mechanism that achieves amortized fairness, where attention accumulated across a series of rankings is proportional to accumulated relevance.We formulate the challenge of achieving amortized individual fairness subject to constraints on ranking quality as an online optimization problem and show that it can be solved as an integer linear program. Our experimental evaluation reveals that unfair attention distribution in rankings can be substantial, and demonstrates that our method can improve individual fairness while retaining high ranking quality.

Sharing economy platforms, such as Airbnb, Uber or eBay, are an increasingly common way for people to provide their services to earn a living. Yet, the focus in these platforms is either on the satisfaction of the customers of the service, or on boosting successful business transactions. However, recent studies provide a multitude of reasons to worry about the providers in the sharing economy ecosystems. The concerns range from bad working conditions and worker manipulation to discrimination against minorities. This is worsened by the fact that the algorithms used for matching customers and providers, that de facto decide the amount of exposure each provider receives, are proprietary and non-transparent. In this position paper, we propose a novel framework to think about fairness in the matching mechanisms of online sharing economy platforms. Specifically, we focus on various fairness guarantees from the providers' perspective. Our notion of fairness relies on the idea that, spread over time, all providers should receive the amount of exposure proportional to their relevance or the utility they provide. We postulate that by not requiring every match to be fair, but rather distributing the fairness over time, we can (i) give better guarantees in terms of the overall benefit for the providers and the customers, (ii) make use of implementations from a long line of research concerned with fair division of constrained resources. Overall, our work takes the first step towards rethinking fairness in online sharing economy systems with an additional emphasis on the well-being of providers, and provides insights into parallels with well-established practical implementations in other domains.

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There is increasing attention to evaluating the fairness of search system ranking decisions. These metrics often consider the membership of items to particular groups, often identified using protected attributes such as gender or ethnicity. To date, these metrics typically assume the availability and completeness of protected attribute labels of items. However, the protected attributes of individuals are rarely present, limiting the application of fair ranking metrics in large scale systems. In order to address this problem, we propose a sampling strategy and estimation technique for four fair ranking metrics. We formulate a robust and unbiased estimator which can operate even with very limited number of labeled items. We evaluate our approach using both simulated and real world data. Our experimental results demonstrate that our method can estimate this family of fair ranking metrics and provides a robust, reliable alternative to exhaustive or random data annotation.

Article 5(1)(c) of the European Union's General Data Protection Regulation (GDPR) requires that "personal data shall be [...] adequate, relevant, and limited to what is necessary in relation to the purposes for which they are processed ('data minimisation')". To date, the legal and computational definitions of 'purpose limitation' and 'data minimization' remain largely unclear. In particular, the interpretation of these principles is an open issue for information access systems that optimize for user experience through personalization and do not strictly require personal data collection for the delivery of basic service.In this paper, we identify a lack of a homogeneous interpretation of the data minimization principle and explore two operational definitions applicable in the context of personalization. The focus of our empirical study in the domain of recommender systems is on providing foundational insights about the (i) feasibility of different data minimization definitions, (ii) robustness of different recommendation algorithms to minimization, and (iii) performance of different minimization strategies.We find that the performance decrease incurred by data minimization might not be substantial, but that it might disparately impact different users-a finding which has implications for the viability of different formal minimization definitions. Overall, our analysis uncovers the complexities of the data minimization problem in the context of personalization and maps the remaining computational and regulatory challenges.

Online donation platforms help equalize access to opportunity and funding in cases where inequalities exist. In the context of public school education in the United States, for instance, financial inequalities have been shown to be reflected in the educational system, since schools are primarily funded through local property taxes. In response, private charitable donation platforms such as DonorsChoose.org have emerged seeking to alleviate systemic inequalities. Yet, the question remains of how effective these platforms are in redressing existing funding inequalities across school districts. Our analysis of donation data from DonorsChoose shows that such platforms may in fact be ineffective in mitigating existing inequalities or may even exacerbate them. In this paper, we explore how online educational charities could direct more funding towards more impoverished schools without compromising their donors' freedom of choice with respect to donation targets. Seeking to answer this question, we draw on the line of work on choice architectures in behavioral economics and pose a novel research question on the impact of interface design on equity in socio-technical systems. Through controlled experiments, we demonstrate how simple interface design interventions - such as modifying default rankings or displaying additional information about schools - might lead to changes in donation distributions helping platforms direct more funding towards schools in need. Going beyond online educational charities, we hope that our work will bring attention to the role of interface design nudges in the social requirements of online altruism.