Inference of Dynamic Regimes in the Microbiome
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Many studies have been performed to characterize the dynamics and stability of the microbiome across a range of environmental contexts [Costello et al., 2012, Faust et al., 2015]. For example, it is often of interest to identify time intervals within which certain subsets of taxa have an interesting pattern of behavior. Viewed abstractly, these problems often have a flavor not just of time series modeling but also of regime detection, a problem with a rich history across a variety of applications, including speech recognition [Fox et al., 2011], finance [Lee, 2009], EEG analysis [Camilleri et al., 2014], and geophysics [Weatherley and Mora, 2002]. In spite of the parallels, regime detection methods are rarely used in microbiome analysis, most likely due to the fact that references for these methods are scattered across several literatures, descriptions are inaccessible outside limited research communities, and implementations are difficult to come across. We distill the core ideas of different regime detection methods, provide example applications, and share reproducible code, making these techniques more accessible to microbiome researchers. We re-analyze data of Dethlefsen and Relman [2011], a study of the effects of antibiotics on the microbiome, using Classification and Regression Trees (CART) [Breiman et al., 1984], Hidden Markov Models (HMMs) [Rabiner and Juang, 1986], Bayesian nonparametric HMMs [Teh and Jordan, 2010, Fox et al., 2008], mixtures of Gaussian Processes (GPs) [Rasmussen and Ghahramani, 2002], switching dynamical systems [Linderman et al., 2016], and multiple changepoint detection [Fan and Mackey, 2015]. Along the way, we summarize each method, their relevance to the microbiome, and tradeoffs associated with using them. Ultimately, our goal is to describe types of temporal or regime switching structure that can be incorporated into studies of microbiome dynamics.
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