The root mean squared error between true and predicted conditional average treatment effects: $$PEHE = \sqrt{\frac{1}{n} \sum_i (\tau(x^{(i)}) - \hat\tau(x^{(i)}))^2}$$ Requires the true CATEs, so it is only usable with (semi-)synthetic benchmark data such as synth_test or ihdp_test.
pehe(tau_true, tau_pred)A single non-negative number.
Hill, J. L. (2011). Bayesian nonparametric modeling for causal inference. Journal of Computational and Graphical Statistics, 20(1), 217-240.