Key research themes
1. How can System and Difference GMM estimators be effectively applied for dynamic panel data with endogenous regressors and limited time dimensions?
This research area focuses on the development and practical implementation of Generalized Method of Moments (GMM) estimators—particularly Difference GMM and System GMM—for panel data models that feature dynamic components and endogenous regressors. These models typically involve 'small T, large N' panels with fixed effects and serial correlation. The critical contributions lie in designing estimators using valid moment conditions, addressing instrument proliferation, correcting finite-sample biases in standard errors, and providing user-friendly implementation through software (e.g., xtabond2). This theme is crucial as these estimators allow consistent and efficient estimation in complex panel data contexts common in economics and finance.
2. What are the advances in efficient and asymptotically optimal GMM estimation using the empirical characteristic function and continuum moment conditions?
This theme explores methodological innovations in GMM estimation that exploit empirical characteristic functions (ECF) to use an infinite continuum of moment conditions. Traditional GMM approaches often rely on finite grids approximating this continuum, leading to inefficiencies or identification issues. By directly utilizing the full continuum and adding penalization terms, these methods achieve asymptotic efficiency closer to the Cramér-Rao lower bound, with practical solutions for tuning parameter selection and specification testing. Such advancements expand GMM applicability, especially in models without tractable likelihoods, enhancing estimation precision and robustness.
3. How can GMM-based latent variable and mixture models be evaluated and extended to improve model fit and clustering in heterogeneous data?
In this research area, GMM estimation is integrated with mixture and latent variable models such as mixtures of generalized linear models (GLMs) or generalized estimating equations (GEE). The aim is to extend classical GMM to handle data heterogeneity and clustering by building mixtures of models and evaluating model fit using deviance-based measures adapted to mixture contexts. Approaches also include developing efficient iterative algorithms alternative to EM for parameter estimation, enhancing accuracy and convergence speed. These advances enable modeling complex correlated and clustered data structures more effectively in diverse empirical applications.