Researchers and practitioners often wish to measure treatment effects in settings where units interact via markets and recommendation systems. In these settings, units are affected by certain shared states, like prices, algorithmic recommendations or social signals. We formalize this structure, calling it shared-state interference, and argue that our formulation captures many relevant applied settings. Our key modeling assumption is that individuals' potential outcomes are independent conditional on the shared state. We then prove an extension of a double machine learning (DML) theorem providing conditions for achieving efficient inference under shared-state interference. We also instantiate our general theorem in several models of interest where it is possible to efficiently estimate the average direct effect (ADE) or global average treatment effect (GATE).

Researchers and practitioners often wish to measure causal effects in recommendation systems or markets, where units interact via centralized information, prices or other shared states. We develop theory allowing for estimation of causal effects in these settings without imposing strict assumptions on the data generating process while preserving the asymptotic efficiency of our method. This allows for valid and efficient inference in important, socially salient settings that was not possible before.