Estimating Causal Effects in Networks with Cluster-Based Bandits

TL;DR

This paper introduces cluster-based multi-armed bandit algorithms to efficiently estimate causal effects in social networks with interference, balancing exploration and exploitation to improve reward while maintaining accurate treatment effect estimation.

Contribution

The paper proposes novel cluster-based MAB algorithms that adaptively learn treatment effects in networks with interference, outperforming traditional RCTs and vanilla bandits in reward and accuracy.

Findings

Cluster-based MAB algorithms achieve higher reward-action ratios.

They maintain accurate treatment effect estimates despite interference.

Compared to RCTs, the algorithms reduce treatment effect error.

Abstract

The gold standard for estimating causal effects is randomized controlled trial (RCT) or A/B testing where a random group of individuals from a population of interest are given treatment and the outcome is compared to a random group of individuals from the same population. However, A/B testing is challenging in the presence of interference, commonly occurring in social networks, where individuals can impact each others outcome. Moreover, A/B testing can incur a high performance loss when one of the treatment arms has a poor performance and the test continues to treat individuals with it. Therefore, it is important to design a strategy that can adapt over time and efficiently learn the total treatment effect in the network. We introduce two cluster-based multi-armed bandit (MAB) algorithms to gradually estimate the total treatment effect in a network while maximizing the expected reward by making a tradeoff between exploration and exploitation. We compare the performance of our MAB algorithms with a vanilla MAB algorithm that ignores clusters and the corresponding RCT methods on semi-synthetic data with simulated interference. The vanilla MAB algorithm shows higher reward-action ratio at the cost of higher treatment effect error due to undesired spillover. The cluster-based MAB algorithms show higher reward-action ratio compared to their corresponding RCT methods without sacrificing much accuracy in treatment effect estimation.