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Published online by Cambridge University Press: 15 February 2024
Cointegrating polynomial regressions (CPRs) include deterministic variables, integrated variables, and their powers as explanatory variables. Based on a novel kernel-weighted limit result and a novel functional central limit theorem, this paper shows that the fully modified ordinary least squares (FM-OLS) estimator of Phillips and Hansen (1990, Review of Economic Studies 57, 99–125) is robust to being used in CPRs. Being used in CPRs refers to a widespread empirical practice that treats the integrated variables and their powers, incorrectly, as a vector of integrated variables and uses textbook FM-OLS. Robustness means that this “formal” FM-OLS practice leads to a zero mean Gaussian mixture limiting distribution that coincides with the limiting distribution of the Wagner and Hong (2016, Econometric Theory 32, 1289–1315) application of the FM estimation principle to the CPR case. The only restriction for this result to hold is that all integrated variables to power one are included as regressors. Even though simulation results indicate performance advantages of the Wagner and Hong (2016, Econometric Theory 32, 1289–1315) estimator, partly even in large samples, the results of the paper give an asymptotic foundation to “formal” FM-OLS and thus enlarge the usability of the Phillips and Hansen (1990, Review of Economic Studies 57, 99–125) estimator implemented in many software packages.
All authors acknowledge partial financial support from the Collaborative Research Center 823: Statistical Modelling of Nonlinear Dynamic Processes supported by the Deutsche Forschungsgemeinschaft (DFG). Martin Wagner furthermore acknowledges research support from the Jubilaumsfonds of the Oesterreichische Nationalbank via several grants. We gratefully acknowledge the helpful comments of, in particular, the editor Peter C. B. Phillips, as well as of a co-editor and four reviewers. We furthermore are grateful for the many comments received from participants in numerous conferences and seminars since 2016. This paper solely reflects the views of the authors and not necessarily those of Flossbach von Storch, the Bank of Slovenia, or the European System of Central Banks. On top of this, the usual disclaimer applies.