Fairness in Rankings

Künstliche Intelligenz und selbst-lernende Systeme, die ihr Verhalten aufgrund vergangener Entscheidungen und historischer Daten adaptieren, spielen eine im- mer größer werdende Rollen in unserem Alltag. Wir sind umgeben von einer großen Zahl algorithmischer Entscheidungshilfen, sowie einer stetig wachsenden Zahl algorithmischer Entscheidungssysteme. Rankings und sortierte Listen von Suchergebnissen stellen dabei das wesentliche Instrument unserer Onlinesuche nach Inhalten, Produkten, Freizeitaktivitäten und relevanten Personen dar. Aus diesem Grund bestimmt die Reihenfolge der Suchergebnisse nicht nur die Zufriedenheit der Suchenden, sondern auch die Chancen der Sortierten auf Bildung, ökonomischen und sogar sozialen Erfolg. Wissenschaft und Politik sorgen sich aus diesem Grund mehr und mehr um systematische Diskriminierung und Bias durch selbst-lernende Systeme. Um der Diskriminierung im Kontext von Rankings und sortierten Suchergeb- nissen Herr zu werden, sind folgende drei Probleme zu addressieren: Zunächst müssen wir die ethischen Eigenschaften und moralischen Ziele verschiedener Sit- uationen erarbeiten, in denen Rankings eingesetzt werden. Diese sollen mit den ethischen Werten der Algorithmen übereinstimmen, die zur Vermeidung von diskri- minierenden Rankings Anwendung finden. Zweitens ist es notwendig, ethische Wertesysteme in Mathematik und Algorithmen zu übersetzen, um sämtliche moralis- chen Ziele bedienen zu können. Drittens sollten diese Methoden einem breiten Publikum zugänglich sein, das sowohl Programmierer:innen, als auch Jurist:innen und Politiker:innen umfasst.Artificial intelligence and adaptive systems, that learn patterns from past behavior and historic data, play an increasing role in our day-to-day lives. We are surrounded by a vast amount of algorithmic decision aids, and more and more by algorithmic decision making systems, too. As a subcategory, ranked search results have become the main mechanism, by which we find content, products, places, and people online. Thus their ordering contributes not only to the satisfaction of the searcher, but also to career and business opportunities, educational placement, and even social success of those being ranked. Therefore researchers have become increasingly concerned with systematic biases and discrimination in data-driven ranking models. To address the problem of discrimination and fairness in the context of rank- ings, three main problems have to be solved: First, we have to understand the philosophical properties of different ranking situations and all important fairness definitions to be able to decide which method would be the most appropriate for a given context. Second, we have to make sure that, for any fairness requirement in a ranking context, a formal definition that meets such requirements exists. More concretely, if a ranking context, for example, requires group fairness to be met, we need an actual definition for group fairness in rankings in the first place. Third, the methods together with their underlying fairness concepts and properties need to be available to a wide range of audiences, from programmers, to policy makers and politicians

Matching Code and Law: Achieving Algorithmic Fairness with Optimal Transport

Increasingly, discrimination by algorithms is perceived as a societal and legal problem. As a response, a number of criteria for implementing algorithmic fairness in machine learning have been developed in the literature. This paper proposes the Continuous Fairness Algorithm (CFA$\theta$) which enables a continuous interpolation between different fairness definitions. More specifically, we make three main contributions to the existing literature. First, our approach allows the decision maker to continuously vary between specific concepts of individual and group fairness. As a consequence, the algorithm enables the decision maker to adopt intermediate ``worldviews'' on the degree of discrimination encoded in algorithmic processes, adding nuance to the extreme cases of ``we're all equal'' (WAE) and ``what you see is what you get'' (WYSIWYG) proposed so far in the literature. Second, we use optimal transport theory, and specifically the concept of the barycenter, to maximize decision maker utility under the chosen fairness constraints. Third, the algorithm is able to handle cases of intersectionality, i.e., of multi-dimensional discrimination of certain groups on grounds of several criteria. We discuss three main examples (credit applications; college admissions; insurance contracts) and map out the legal and policy implications of our approach. The explicit formalization of the trade-off between individual and group fairness allows this post-processing approach to be tailored to different situational contexts in which one or the other fairness criterion may take precedence. Finally, we evaluate our model experimentally.Comment: Vastly extended new version, now including computational experiment

FairSearch: a tool for fairness in ranked search results

Comunicació presentada al WWW'20: International World Wide Web Conference, celebrat del 20 al 24 d'abril de 2020 a Taipei, Taiwan.Ranked search results and recommendations have become the main mechanism by which we find content, products, places, and people online. With hiring, selecting, purchasing, and dating being increasingly mediated by algorithms, rankings may determine business opportunities, education, access to benefits, and even social success. It is therefore of societal and ethical importance to ask whether search results can demote, marginalize, or exclude individuals of unprivileged groups or promote products with undesired features. In this paper we present FairSearch, the first fair open source search API to provide fairness notions in ranked search results. We implement two well-known algorithms from the literature, namely FA*IR (Zehlike et al., 9) and DELTR (Zehlike and Castillo, 10) and provide them as stand-alone libraries in Python and Java. Additionally we implement interfaces to Elasticsearch for both algorithms, a well-known search engine API based on Apache Lucene. The interfaces use the aforementioned Java libraries and enable search engine developers who wish to ensure fair search results of different styles to easily integrate DELTR and FA*IR into their existing Elasticsearch environment.This project was realized with a research grant from Data Transparency Lab. Castillo is partially funded by La Caixa project LCF/PR/PR16/11110009. Zehlike is funded by the MPI-SWS

FA*IR: a fair top-k ranking algorithm

Comunicació presentada a: CIKM '17 Conference on Information and Knowledge Management, celebrada del 6 al 10 de novembre de 2017 a Singapur, Singapur.In this work, we define and solve the Fair Top-k Ranking problem, in which we want to determine a subset of k candidates from a large pool of n>>k candidates, maximizing utility (i.e., select the “best” candidates) subject to group fairness criteria. Our ranked group fairness de nition extends group fairness using the standard notion of protected groups and is based on ensuring that the proportion of protected candidates in every pre x of the top-k ranking remains statistically above or indistinguishable from a given minimum. Utility is operationalized in two ways: (i) every candidate included in the top-k should be more quali ed than every candidate not included; and (ii) for every pair of candidates in the top-k, the more qualified candidate should be ranked above. An efficient algorithm is presented for producing the Fair Top-k Ranking, and tested experimentally on existing datasets as well as new datasets released with this paper, showing that our approach yields small distortions with respect to rankings that maximize utility without considering fairness criteria. To the best of our knowledge, this is the first algorithm grounded in statistical tests that can mitigate biases in the representation of an under-represented group along a ranked list.This research was supported by the German Research Foundation, Eurecat and the Catalonia Trade and Investment Agency (ACCIÓ). M.Z. and M.M. were supported by the GRF. C.C. and S.H. worked on this paper while at Eurecat. C.C., S.H., and F.B. were supported by ACCIÓ

FA*IR: a fair top-k ranking algorithm

Comunicació presentada a: CIKM '17 Conference on Information and Knowledge Management, celebrada del 6 al 10 de novembre de 2017 a Singapur, Singapur.In this work, we define and solve the Fair Top-k Ranking problem, in which we want to determine a subset of k candidates from a large pool of n>>k candidates, maximizing utility (i.e., select the “best” candidates) subject to group fairness criteria. Our ranked group fairness de nition extends group fairness using the standard notion of protected groups and is based on ensuring that the proportion of protected candidates in every pre x of the top-k ranking remains statistically above or indistinguishable from a given minimum. Utility is operationalized in two ways: (i) every candidate included in the top-k should be more quali ed than every candidate not included; and (ii) for every pair of candidates in the top-k, the more qualified candidate should be ranked above. An efficient algorithm is presented for producing the Fair Top-k Ranking, and tested experimentally on existing datasets as well as new datasets released with this paper, showing that our approach yields small distortions with respect to rankings that maximize utility without considering fairness criteria. To the best of our knowledge, this is the first algorithm grounded in statistical tests that can mitigate biases in the representation of an under-represented group along a ranked list.This research was supported by the German Research Foundation, Eurecat and the Catalonia Trade and Investment Agency (ACCIÓ). M.Z. and M.M. were supported by the GRF. C.C. and S.H. worked on this paper while at Eurecat. C.C., S.H., and F.B. were supported by ACCIÓ

Evaluating Stochastic Rankings with Expected Exposure

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