Document Type
Discussion Paper
Publication Date
10-1-2012
CFDP Number
1880
CFDP Pages
24
Abstract
In this note, we characterize the semiparametric efficiency bound for a class of semiparametric models in which the unknown nuisance functions are identified via nonparametric conditional moment restrictions with possibly non-nested or over-lapping conditioning sets, and the finite dimensional parameters are potentially over-identified via unconditional moment restrictions involving the nuisance functions. We discover a surprising result that semiparametric two-step optimally weighted GMM estimators achieve the efficiency bound, where the nuisance functions could be estimated via any consistent nonparametric procedures in the first step. Regardless of whether the efficiency bound has a closed form expression or not, we provide easy-to-compute sieve based optimal weight matrices that lead to asymptotically efficient two-step GMM estimators.
Recommended Citation
Chen, Xiaohong; Hahn, Jinyong; and Liao, Zhipeng, "Asymptotic Efficiency of Semiparametric Two-step GMM" (2012). Cowles Foundation Discussion Papers. 2248.
https://elischolar.library.yale.edu/cowles-discussion-paper-series/2248