A4 Refereed article in a conference publication 
A Hierarchical Ornstein-Uhlenbeck Model for Stochastic Time Series Analysis
Authors: Laitinen V., Lahti L.
Editors: Wouter Duivesteijn, Arno Siebes, Antti Ukkonen
Conference name: International Symposium on Intelligent Data Analysis
Publisher: Springer Verlag
Publication year: 2018
Journal:Lecture Notes in Computer Science
Book title : Advances in Intelligent Data Analysis XVII: 17th International Symposium, IDA 2018, ’s-Hertogenbosch, The Netherlands, October 24–26, 2018, Proceedings
Journal name in sourceLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Series title: Lecture Notes in Computer Science
Volume: 11191
First page : 188
Last page: 199
ISBN: 978-3-030-01767-5
eISBN: 978-3-030-01768-2
ISSN: 0302-9743
DOI: https://doi.org/10.1007/978-3-030-01768-2_16
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/36542525
Longitudinal data is ubiquitous in research, and often complemented by 
broad collections of static background information. There is, however, a
 shortage of general-purpose statistical tools for studying the temporal
 dynamics of complex and stochastic dynamical systems especially when 
data is scarce, and the underlying mechanisms that generate the 
observation are poorly understood. Contemporary microbiome research 
provides a topical example, where vast cross-sectional and longitudinal 
collections of taxonomic profiling data from the human body and other 
environments are now being collected in various research laboratories 
world-wide. Many classical algorithms rely on long and densely sampled 
time series, whereas human microbiome studies typically have more 
limited sample sizes, short time spans, sparse sampling intervals, lack 
of replicates and high levels of unaccounted technical and biological 
variation. We demonstrate how non-parametric models can help to quantify
 key properties of a dynamical system when the actual data-generating 
mechanisms are largely unknown. Such properties include the locations of
 stable states, resilience of the system, and the levels of stochastic 
fluctuations. Moreover, we show how limited data availability can be 
compensated by pooling statistical evidence across multiple individuals 
or studies, and by incorporating prior information in the models. In 
particular, we derive and implement a hierarchical Bayesian variant of 
Ornstein-Uhlenbeck driven t-processes. This can be used to characterize 
universal dynamics in univariate, unimodal, and mean reversible systems 
based on multiple short time series. We validate the model with 
simulated data and investigate its applicability in characterizing 
temporal dynamics of human gut microbiome.
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