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Optimal Cross-Sectional Regression

In the context of linear-beta pricing models, we develop a new class of two-pass estimators that 
are available in closed form and dominate existing two-pass estimators in terms of estimation 
efficiency. Importantly, we map our model into the generalized method of moments (GMM) 
framework and show our two-pass estimator is as efficient as the optimal GMM estimator, 
which is known to be semiparametrically efficient in the literature. Hence, contrary to popular 
belief, information loss does not need to occur when we go from the more methodical GMM 
approach to the simple-to-implement two-pass regressors. Intuitively, our estimator improves 
efficiency by disentangling the impacts of idiosyncratic and systematic return innovations on 
pricing errors in the second-stage cross-sectional regression. As an empirical application of the 
new two-pass estimators, we apply our approach to current factor models and shed new light 
on the Fama and French (2015) versus Hou, Xue, and Zhang (2015) debate.