Model robust hybrid likelihood

Abstract: The article concerns hybrid combinations of empirical and parametric likelihood functions. Combining the two allows classical parametric likelihood to be crucially modified via the nonparametric counterpart, making possible model misspecification less problematic. Limit theory for the maximum hybrid likelihood estimator is sorted out, also outside the parametric model conditions. Results include consistency of the estimated parameter in the parametric model towards a well-defined limit, as well as asymptotic normality after proper scaling and centring of the same quantity. Our results allow for the presence of plug-in parameters in the hybrid and empirical likelihood framework. Furthermore, the variance and mean squared error of these estimators are studied, with recipes for their estimation. The latter is used to define a focused information criterion, which can be used to choose how the parametric and empirical part of the hybrid combination should be balanced. This allows for hybrid models to be fitted in a context driven way, minimizing the estimated mean squared error for estimating any pre-specified quantity of interest.