A test of the selection on observables assumption using a discontinuously distributed covariate
利用分布不连续协变量检验基于可观测变量的选择假设
We present a test of the selection on observables assumption that neither requires instruments nor excluded covariates from the structural function. Instead, we rely on the presence of a discontinuously distributed variable among the set of controls. We develop formal testing procedures for a non-parametric additively separable model for binary and finite treatment variables. We also outline a nonparametric nonseparable extension. Our test is easy to implement and should be…