Generalized Covariance Estimator under Misspecification and Constraints

This paper investigates the properties of the Generalized Covariance (GCov) estimator under misspecification and constraints with application to processes with local explosive patterns, such as causal-noncausal and double autoregressive (DAR) processes. We show that GCov is consistent and has an asymptotically Normal distribution under misspecification. Then, we construct GCov-based Wald-type and score-type tests to test one specification against the other, all of which follow a $\chi^2$ distribution. Furthermore, we propose the constrained GCov (CGCov) estimator, which extends the use of the GCov estimator to a broader range of models with constraints on their parameters. We investigate the asymptotic distribution of the CGCov estimator when the true parameters are far from the boundary and on the boundary of the parameter space. We validate the finite sample performance of the proposed estimators and tests in the context of causal-noncausal and DAR models. Finally, we provide two empirical applications by applying the noncausal model to the final energy demand commodity index and also the DAR model to the US 3-month treasury bill.