Published online by Cambridge University Press: 07 January 2020
There are many environments in econometrics which require nonseparable modeling of a structural disturbance. In a nonseparable model with endogenous regressors, key conditions are validity of instrumental variables and monotonicity of the model in a scalar unobservable variable. Under these conditions the nonseparable model is equivalent to an instrumental quantile regression model. A failure of the key conditions, however, makes instrumental quantile regression potentially inconsistent. This article develops a methodology for testing the hypothesis whether the instrumental quantile regression model is correctly specified. Our test statistic is asymptotically normally distributed under correct specification and consistent against any alternative model. In addition, test statistics to justify the model simplification are established. Finite sample properties are examined in a Monte Carlo study and an empirical illustration is provided.
Parts of this article derive from my doctoral dissertation, completed under the guidance of Enno Mammen. I would like to thank Liangjun Su and four anonymous referees for excellent comments and suggestions that greatly improved the article. I also thank seminar participants at Boston College, Bristol, Mannheim, Toulouse School of Economics, University College London, WIAS Berlin, and Yale. I am also grateful for the support and hospitality of the Cowles Foundation.