Bayesian Gaussian Process Models for Flexible Conway-Maxwell Poisson Regression
DOI:
https://doi.org/10.31185/bsj.Vol22.Iss43.1666Keywords:
Keywords: Conway-Maxwell-Poisson (COM-Poisson), Gaussian Process Regression, Bayesian Non-parametric, Count Data, Over-dispersion, Under-dispersion, Hierarchical Bayesian Model, Markov Chain Monte Carlo (MCMC).Abstract
In quantitative science, regression models for count data are essential. Also, strict distributional assumptions limit standard methods. While solutions such as Negative Binomial regression address over-dispersion, they do not account for under-dispersion. Which is another common violation of the Poisson model's equidispersion assumption. A strong generalization that can model both phenomena is provided by Conway-Maxwell-Poisson (COM-Poisson) distribution. Another significant drawback is that it is implemented within Generalized Linear Model (GLM) framework. Also more complex, non-linear dependencies cannot be captured because it assumes log-linear relationships between covariates. Where including the rate (λ) also dispersion (v) parameters. In order to close this gap, a novel fully Bayesian non-parametric framework is introduced in this paper. Where the Gaussian Process COM-Poisson (GP-COM-Poisson) regression model.
The link functions of the rate and dispersion parameters are subject to independent Gaussian Process priors. Where letting them fluctuate as non-linear, smooth functions of covariates where model can simultaneously capture intricate functional relationships straight from the data. Also account for arbitrary dispersion thanks to this structure, Hamiltonian Monte Carlo (HMC) is used for inference, effective for GP models'high-dimensional posteriors. When compared to parametric and semi-parametric alternatives. It exhibits better performance in both function recovery (MSE) and predictive fit (WAIC) where usefulness of the model is further demonstrated by a real-data application to the ecological dataset of the Galápagos Islands. Where revealing a new covariate-driven heterogeneity in dispersion in addition to a non-linear impact of elevation on species richness. A strong and adaptable addition to the statistical toolbox is the GP-COM-Poisson model. Where more thorough and trustworthy explanations of intricate count data phenomena are provided.
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