Quantile Multi-Armed Bandits: Optimal Best-Arm Identification and a Differentially Private Scheme

• URL: http://arxiv.org/abs/2006.06792v3
• Date: Sun, 23 May 2021 23:08:14 GMT
• Title: Quantile Multi-Armed Bandits: Optimal Best-Arm Identification and a Differentially Private Scheme
• Authors: Kontantinos E. Nikolakakis, Dionysios S. Kalogerias, Or Sheffet and Anand D. Sarwate
• Abstract summary: We study the best-arm identification problem in multi-armed bandits with, potentially private rewards. The goal is to identify the arm with the highest quantile at a fixed, prescribed level. We show that our algorithm is $delta$-PAC and we characterize its sample complexity.
• Score: 16.1694012177079
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: We study the best-arm identification problem in multi-armed bandits with stochastic, potentially private rewards, when the goal is to identify the arm with the highest quantile at a fixed, prescribed level. First, we propose a (non-private) successive elimination algorithm for strictly optimal best-arm identification, we show that our algorithm is $\delta$-PAC and we characterize its sample complexity. Further, we provide a lower bound on the expected number of pulls, showing that the proposed algorithm is essentially optimal up to logarithmic factors. Both upper and lower complexity bounds depend on a special definition of the associated suboptimality gap, designed in particular for the quantile bandit problem, as we show when the gap approaches zero, best-arm identification is impossible. Second, motivated by applications where the rewards are private, we provide a differentially private successive elimination algorithm whose sample complexity is finite even for distributions with infinite support-size, and we characterize its sample complexity. Our algorithms do not require prior knowledge of either the suboptimality gap or other statistical information related to the bandit problem at hand.

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