A corrected formulation for marginal inference derived from two-part mixed models for longitudinal semi-continuous data.

ABSTRACT: For semi-continuous data which are a mixture of true zeros and continuously distributed positive values, the use of two-part mixed models provides a convenient modelling framework. However, deriving population-averaged (marginal) effects from such models is not always straightforward. Su et al. presented a model that provided convenient estimation of marginal effects for the logistic component of the two-part model but the specification of marginal effects for the continuous part of the model presented in that paper was based on an incorrect formulation. We present a corrected formulation and additionally explore the use of the two-part model for inferences on the overall marginal mean, which may be of more practical relevance in our application and more generally.

SUBMITTER: Tom BD 

PROVIDER: S-EPMC5051603 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature