Many of the data, particularly in medicine and disease mapping are count. Indeed, the under or overdispersion problem in count data distrusts the performance of the classical Poisson model. For taking into account this problem, in this paper, we introduce a new Bayesian structured additive regression model, called gamma count, with enough flexibility in modeling dispersion. Setting convenient prior distributions on the model parameters is a momentous issue in Bayesian statistics that characterize the nature of our uncertainty parameters. Relying on a recently proposed class of penalized complexity priors, motivated from a general set of construction principles, we derive the prior structure. The model can be formulated as a latent Gaussian model, and consequently, we can carry out the fast computation by using the integrated nested Laplace approximation method. We investigate the proposed methodology simulation study. Different expropriate prior distribution are examined to provide reasonable sensitivity analysis. To explain the applicability of the proposed model, we analyzed two real-world data sets related to the larynx mortality cancer in Germany and the handball champions league.
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