The class of inhomogeneous phase‐type distributions (IPH) was recently introduced in Albrecher & Bladt (2019) as an extension of the classical phase‐type (PH) distributions. Like PH distributions, the class of IPH is dense in the class of distributions on the positive halfline, but leads to more parsimonious models in the presence of heavy tails. In this paper we propose a fitting procedure for this class to given data. We furthermore consider an analogous extension of Kulkarni's multivariate PH class (Kulkarni, 1989) to the inhomogeneous framework and study parameter estimation for the resulting new and flexible class of multivariate distributions. As a by‐product, we amend a previously suggested fitting procedure for the homogeneous multivariate PH case and provide appropriate adaptations for censored data. The performance of the algorithms is illustrated in several numerical examples, both for simulated and real‐life insurance data.
We study random variables arising as the product of phase-type distributions and continuous random variables, revisiting their asymptotic properties, and developing an expectation-maximization algorithm for their statistical analysis. Throughout, emphasis is made on closed-form formulas for various functionals of the resulting mixed distributions, which facilitates their analysis and implementation.
Frailty models are survival analysis models which account for heterogeneity and random effects in the data. In these models, the random effect (the frailty) is assumed to have a multiplicative effect on the hazard. In this paper, we present frailty models using phase-type distributions as the frailties. We explore the properties of the proposed frailty models and derive expectation-maximization algorithms for maximum-likelihood estimation. The algorithms' performance is illustrated in several numerical examples of practical significance.
Inhomogeneous phase-type distributions (IPH) are a broad class of laws which arise from the absorption times of Markov jump processes. In the time-homogeneous particular case, we recover phase-type (PH) distributions. In matrix notation, various functionals corresponding to their distributional properties are explicitly available and succinctly described. As the number of parameters increases, IPH distributions may converge weakly to any probability measure on the positive real line, making them particularly attractive candidates for statistical modelling purposes. Contrary to PH distributions, the IPH class allows for a wide range of tail behaviours, which often leads to adequate estimation with a moderate number of parameters. One of the main difficulties in estimating PH and IPH distributions is their large number of matrix parameters. This drawback is best handled through the expectation-maximisation (EM) algorithm, exploiting the underlying and unobserved Markov structure. The matrixdist package presents tools for IPH distributions to efficiently evaluate functionals, simulate, and carry out maximum likelihood estimation through a three-step EM algorithm. Aggregated and right-censored data are supported by the fitting routines, and in particular, one may estimate time-to-event data, histograms, or discretised theoretical distributions.
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