Flexible joint models for multivariate longitudinal and time-to-event data using multivariate functional principal components

TL;DR

This paper introduces a scalable, flexible joint modeling approach for multivariate longitudinal biomarkers and time-to-event data using multivariate functional principal components, enabling nonlinear trajectories without high-dimensional complexity.

Contribution

It proposes a novel multivariate functional principal components method for joint models, improving scalability and flexibility over traditional shared parameter models.

Findings

Enhanced model scalability with fewer random effects.

Ability to estimate nonlinear, individual-specific trajectories.

Validated approach through simulation and real data analysis.

Abstract

The joint modeling of multiple longitudinal biomarkers together with a time-to-event outcome is a challenging modeling task of continued scientific interest. In particular, the computational complexity of high dimensional (generalized) mixed effects models often restricts the flexibility of shared parameter joint models, even when the subject-specific marker trajectories follow highly nonlinear courses. We propose a parsimonious multivariate functional principal components representation of the shared random effects. This allows better scalability, as the dimension of the random effects does not directly increase with the number of markers, only with the chosen number of principal component basis functions used in the approximation of the random effects. The functional principal component representation additionally allows to estimate highly flexible subject-specific random trajectories without parametric assumptions. The modeled trajectories can thus be distinctly different for each biomarker. We build on the framework of flexible Bayesian additive joint models implemented in the R-package 'bamlss', which also supports estimation of nonlinear covariate effects via Bayesian P-splines. The flexible yet parsimonious functional principal components basis used in the estimation of the joint model is first estimated in a preliminary step. We validate our approach in a simulation study and illustrate its advantages by analyzing a study on primary biliary cholangitis.