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Journal Article

Latent time-varying factors in longitudinal analysis: a linear mixed hidden Markov model for heart rates

Lagona, F., Jdanov, D. A., Shkolnikova, M. A.

Statistics in Medicine, 33:23, 4116-4134 (2014)

DOI:10.1002/sim.6220

Keywords: Russian Federation, cardiovascular system, Markov chains

Abstract

Longitudinal data are often segmented by unobserved time-varying factors, which introduce latent heterogeneity at the observation level, in addition to heterogeneity across subjects. We account for this latent structure by a linear mixed hidden Markov model. It integrates subject-specific random effects and Markovian sequences of time-varying effects in the linear predictor. We propose an expectation┼░-maximization algorithm for maximum likelihood estimation, based on data augmentation. It reduces to the iterative maximization of the expected value of a complete likelihood function, derived from an augmented dataset with case weights, alternated with weights updating. In a case study of the Survey on Stress Aging and Health in Russia, the model is exploited to estimate the influence of the observed covariates under unobserved time-varying factors, which affect the cardiovascular activity of each subject during the observation period.

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