Optimal Maximin GMM Tests for Sphericity in Latent Factor Analysis of Short Panels
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Series
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Speaker(s)Patrick Gagliardini (University of Lugano, Switzerland)
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FieldEconometrics, Data Science and Econometrics
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LocationErasmus University Rotterdam, Campus Woudestein, ET-14
Rotterdam -
Date and time
October 22, 2025
12:00 - 13:00
Abstract
We derive optimal maximin tests for parametric hypotheses in short panels with latent common factors. We rely on a Generalized Method of Moments setting with optimal weighting under a large cross-sectional dimension n and a fixed time series dimension T. We outline the asymptotic distributions of the estimators as well as the asymptotic maximin optimality of the Wald, Lagrange Multiplier, and Likelihood Ratio-type tests. The characterisation of optimality relies on finding the limit Gaussian experiment in strongly identified GMM models under a block-dependence structure and unobserved heterogeneity. We reject sphericity of idiosyncratic errors in an empirical application to a large cross-section of U.S. stocks, which casts doubt on the validity of routinely applying Principal Component Analysis to short panels of monthly financial returns.
Joint paper with Alain-Philippe Fortin, Patrick Gagliardini, Olivier Scaillet.