Скачать или смотреть Eric Tchetgen Tchetgen: Revisiting Identification in the Binary IV Model: the NATE and Beyond

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Tuesday, Feb 18, 2025: Eric Tchetgen Tchetgen (University of Pennsylvania)
Title: Revisiting Identification in the Binary Instrumental Variable Model: the NATE and Beyond
Abstract: This talk revisits the identification problem in the canonical binary instrumental variable model. The work reveals new conditions for the classical Wald ratio estimand (WR) to be endowed with a nonparametric causal interpretation. Specifically, we describe a straightforward set of conditions under which the Wald Ratio point identifies the Nudge Average Treatment Effect (NATE), defined as the average causal effect for the subgroup of units whose treatment can be manipulated by the instrument, a sub-group referred to as Nudge-able. Crucially, the nudge-able may include both compliers and defiers therefore obviating the need for the standard no-defier IV condition known to identify the Local Average Treatment Effect. Our key identification condition for the NATE is that any variability of the treatment effect induced by a hidden counfounder must be is uncorrelated with corresponding variability in the share of compliers among the Nudge-able. An important and easily interpretable sufficient condition for this assumption is that, although a priori unrestricted, the share of compliers within the subgroup of nudge-able units is balanced across strata of the unmeasured confounders. We will also describe various generalizations of our results, including new straightforward conditions for identification of the average treatment effect for the treated by a generalized Wald ratio estimand, together with new quasi-IV identification results with an imperfect instrument which violates the exclusion restriction assumption.