On the role of parametrization in models with a misspecified nuisance component

The paper is concerned with inference for a parameter of interest in models that share a common interpretation for that parameter, but that may differ appreciably in other respects. We study the general structure of models under which the maximum likelihood estimator of the parameter of interest is consistent under arbitrary misspecification of the nuisance part of the model. A specialization of the general results to matched-comparison and two-groups problems gives a more explicit condition in terms of a new notion of symmetric parametrization, leading to an appreciable broadening and unification of existing results in those problems. The role of a generalized definition of parameter orthogonality is highlighted, as well as connections to Neyman orthogonality. The issues involved in obtaining inferential guarantees beyond consistency are discussed.