A Statistical Approach to the Alignment of fMRI Data

Multi-subject functional Magnetic Resonance Image studies are critical. The anatomical and functional structure varies across subjects, so the image alignment is necessary. We define a probabilistic model to describe functional alignment. Imposing a prior distribution, as the matrix Fisher Von Mises distribution, of the orthogonal transformation parameter, the anatomical information is embedded in the estimation of the parameters, i.e., penalizing the combination of spatially distant voxels. Real applications show an improvement in the classification and interpretability of the results compared to various functional alignment methods

A comparison of the CAR and DAGAR spatial random effects models with an application to diabetics rate estimation in Belgium

When hierarchically modelling an epidemiological phenomenon on a finite collection of sites in space, one must always take a latent spatial effect into account in order to capture the correlation structure that links the phenomenon to the territory. In this work, we compare two autoregressive spatial models that can be used for this purpose: the classical CAR model and the more recent DAGAR model. Differently from the former, the latter has a desirable property: its ρ parameter can be naturally interpreted as the average neighbor pair correlation and, in addition, this parameter can be directly estimated when the effect is modelled using a DAGAR rather than a CAR structure. As an application, we model the diabetics rate in Belgium in 2014 and show the adequacy of these models in predicting the response variable when no covariates are available

Sampling designs via a multivariate hypergeometric-Dirichlet process model for a multi-species assemblage with unknown heterogeneity

In a sample of mRNA species counts, sequences without duplicates or with small numbers of copies are likely to carry information related to mutations or diseases and can be of great interest. However, in some situations, sequence abundance is unknown and sequencing the whole sample to find the rare sequences is not practically possible. To collect mRNA sequences of interest, or more generally, species of interest, we propose a two-phase Bayesian sampling method that addresses these concerns. The first phase of the design is used to infer sequence (species) abundance levels through a cluster analysis applied to a pilot data set. The clustering method is built upon a multivariate hypergeometric model with a Dirichlet process prior for species relative frequencies. The second phase, through Monte Carlo simulations, infers the sample size necessary to collect a certain number of species of particular interest. Efficient posterior computing schemes are proposed. The developed approach is demonstrated and evaluated via simulations. An mRNA segment data set is used to illustrate and motivate the proposed sampling method. © 2012 Elsevier B.V. All rights reserved

Sampling designs via a multivariate hypergeometric-Dirichlet process model for a multi-species assemblage with unknown heterogeneity

In a sample of mRNA species counts, sequences without duplicates or with small numbers of copies are likely to carry information related to mutations or diseases and can be of great interest. However, in some situations, sequence abundance is unknown and sequencing the whole sample to find the rare sequences is not practically possible. To collect mRNA sequences of interest, or more generally, species of interest, we propose a two-phase Bayesian sampling method that addresses these concerns. The first phase of the design is used to infer sequence (species) abundance levels through a cluster analysis applied to a pilot data set. The clustering method is built upon a multivariate hypergeometric model with a Dirichlet process prior for species relative frequencies. The second phase, through Monte Carlo simulations, infers the sample size necessary to collect a certain number of species of particular interest. Efficient posterior computing schemes are proposed. The developed approach is demonstrated and evaluated via simulations. An mRNA segment data set is used to illustrate and motivate the proposed sampling method. © 2012 Elsevier B.V. All rights reserved