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Published online by Cambridge University Press: 24 April 2023
We propose various semiparametric estimators for nonlinear selection models, where slope and intercept can be separately identified. When the selection equation satisfies a monotonic index restriction, we suggest a local polynomial estimator, using only observations for which the marginal cumulative distribution function of the instrument index is close to one. Data-driven procedures such as cross-validation may be used to select the bandwidth for this estimator. We then consider the case in which the monotonic index restriction does not hold and/or the set of observations with a propensity score close to one is thin so that convergence occurs at a rate that is arbitrarily close to the cubic rate. We explore the finite sample behavior in a Monte Carlo study and illustrate the use of our estimator using a model for count data with multiplicative unobserved heterogeneity.
We are grateful to the Editor (Peter Phillips), the Co-Editor (Simon Lee), and three anonymous referees for their very useful and constructive comments. We also thank Christoph Breunig, Sarawata Chaudhuri, Xavier D’Haultfoeuille, Prosper Dovonon, Jean-Marie Dufour, Bernd Fitzenberger, Mathieu Marcoux, Jeff Racine, Joao Santos Silva, Victoria Zinde-Walsh, and seminar participants at the ESEM 2018, Kent, Frankfurt, ISNPS 2018, Surrey, Concordia University-Cireq, Humboldt University Berlin, the Econometrics Study Group Meeting in Bristol 2017, and ESEM 2017 for useful comments and suggestions.