$α$-Fair Contextual Bandits
This addresses fairness concerns in applications like recommender systems and clinical trials to avoid echo-chamber effects and meet regulatory requirements, representing an incremental advancement by adapting existing bandit frameworks to a fairness objective.
The paper tackles the problem of ensuring fairness in contextual bandit algorithms by maximizing an α-fair utility function instead of cumulative rewards, and it designs an efficient algorithm that guarantees approximately sublinear regret in adversarial settings with full-information and bandit feedback.
Contextual bandit algorithms are at the core of many applications, including recommender systems, clinical trials, and optimal portfolio selection. One of the most popular problems studied in the contextual bandit literature is to maximize the sum of the rewards in each round by ensuring a sublinear regret against the best-fixed context-dependent policy. However, in many applications, the cumulative reward is not the right objective - the bandit algorithm must be fair in order to avoid the echo-chamber effect and comply with the regulatory requirements. In this paper, we consider the $α$-Fair Contextual Bandits problem, where the objective is to maximize the global $α$-fair utility function - a non-decreasing concave function of the cumulative rewards in the adversarial setting. The problem is challenging due to the non-separability of the objective across rounds. We design an efficient algorithm that guarantees an approximately sublinear regret in the full-information and bandit feedback settings.