Robust estimation of heterogeneous treatment effects in randomized trials leveraging external data

Rickard K.A. Karlsson, Piersilvio De Bartolomeis, Issa Dahabreh, Jesse H. Krijthe

Keywords: CATE estimation, data fusion, randomized data, violated causal assumptions

TL;DR: We propose a robust CATE learner for improving the efficiency of CATE estimation in a randomised trial with the help of external data.

Abstract: Randomized trials are typically designed to detect average treatment effects but often lack the statistical power to uncover individual-level treatment effect heterogeneity, limiting their value for personalized decision-making. To address this, we propose the QR-learner, a model-agnostic learner that estimates conditional average treatment effects (CATE) within the trial population by leveraging external data from other trials or observational studies. The method is robust: it has the potential to reduce the CATE prediction mean squared error while maintaining consistency, even when the external data is not aligned with the trial. We examine the performance of our approach in simulation studies, and find that it is robust and reduces CATE estimation mean-squared error.

Submission Number: 38