A Mixed Model Approach for Geoadditive Hazard Regression

. Mixed model based approaches for semiparametric regression have gained much interest in recent years, both in theory and application. They provide a unified and modular framework for penalized likelihood and closely related empirical Bayes inference. In this article, we develop mixed model methodology for a broad class of Cox‐type hazard regression models where the usual linear predictor is generalized to a geoadditive predictor incorporating non‐parametric terms for the (log‐)baseline hazard rate, time‐varying coefficients and non‐linear effects of continuous covariates, a spatial component, and additional cluster‐specific frailties. Non‐linear and time‐varying effects are modelled through penalized splines, while spatial components are treated as correlated random effects following either a Markov random field or a stationary Gaussian random field prior. Generalizing existing mixed model methodology, inference is derived using penalized likelihood for regression coefficients and (approximate) marginal likelihood for smoothing parameters. In a simulation we study the performance of the proposed method, in particular comparing it with its fully Bayesian counterpart using Markov chain Monte Carlo methodology, and complement the results by some asymptotic considerations. As an application, we analyse leukaemia survival data from northwest England.