Search Results for author: Vitor Hadad

Found 6 papers, 3 papers with code

Contextual Bandits in a Survey Experiment on Charitable Giving: Within-Experiment Outcomes versus Policy Learning

no code implementations22 Nov 2022 Susan Athey, Undral Byambadalai, Vitor Hadad, Sanath Kumar Krishnamurthy, Weiwen Leung, Joseph Jay Williams

We design and implement an adaptive experiment (a ``contextual bandit'') to learn a targeted treatment assignment policy, where the goal is to use a participant's survey responses to determine which charity to expose them to in a donation solicitation.

Multi-Armed Bandits

Off-Policy Evaluation via Adaptive Weighting with Data from Contextual Bandits

1 code implementation3 Jun 2021 Ruohan Zhan, Vitor Hadad, David A. Hirshberg, Susan Athey

In particular, when the pattern of treatment assignment in the collected data looks little like the pattern generated by the policy to be evaluated, the importance weights used in DR estimators explode, leading to excessive variance.

Multi-Armed Bandits Off-policy evaluation

Adapting to Misspecification in Contextual Bandits with Offline Regression Oracles

no code implementations26 Feb 2021 Sanath Kumar Krishnamurthy, Vitor Hadad, Susan Athey

Computationally efficient contextual bandits are often based on estimating a predictive model of rewards given contexts and arms using past data.

Multi-Armed Bandits regression

Tractable contextual bandits beyond realizability

no code implementations25 Oct 2020 Sanath Kumar Krishnamurthy, Vitor Hadad, Susan Athey

When realizability does not hold, our algorithm ensures the same guarantees on regret achieved by realizability-based algorithms under realizability, up to an additive term that accounts for the misspecification error.

Multi-Armed Bandits

Confidence Intervals for Policy Evaluation in Adaptive Experiments

1 code implementation7 Nov 2019 Vitor Hadad, David A. Hirshberg, Ruohan Zhan, Stefan Wager, Susan Athey

In this context, typical estimators that use inverse propensity weighting to eliminate sampling bias can be problematic: their distributions become skewed and heavy-tailed as the propensity scores decay to zero.

Experimental Design Multi-Armed Bandits

Sufficient Representations for Categorical Variables

3 code implementations26 Aug 2019 Jonathan Johannemann, Vitor Hadad, Susan Athey, Stefan Wager

Many learning algorithms require categorical data to be transformed into real vectors before it can be used as input.

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