Rethinking Nonlinear Instrumental Variables

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2019

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Abstract

Instrumental variable (IV) models are widely used in the social and health sciences in situations where a researcher would like to measure a causal eect but cannot perform an experiment. Formally checking the assumptions of an IV model with a given dataset is impossible, leading many researchers to take as given a linear functional form and two-stage least squares tting procedure. In this paper, we propose a method for evaluating the validity of IV models using observed data and show that, in some cases, a more flexible nonlinear model can address violations of the IV conditions. We also develop a test that detects violations in the instrument that are present in the observed data. We introduce a new version of the validity check that is suitable for machine learning and provides optimization-based techniques to answer these questions. We demonstrate the method using both the simulated data and a real-world dataset.

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Li, Chunxiao (2019). Rethinking Nonlinear Instrumental Variables. Master's thesis, Duke University. Retrieved from https://hdl.handle.net/10161/18898.

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