A common problem in modeling count data is underdispersion or overdispersion. This paper discusses the distinction between overdispersion due to excess zeros and overdispersion due to values that are greater than 0. It shows how to use exploratory data analysis to determine the dispersion patterns and that the dispersion patterns can change depending on the predictors and the subpopulation that...

The psychometric function describes how an experimental variable, such as stimulus strength, influences the behaviour of an observer. Estimation of psychometric functions from experimental data plays a central role in fields such as psychophysics, experimental psychology and in the behavioural neurosciences. Experimental data may exhibit substantial overdispersion, which may result from non-sta...

Although protein evolution can be approximated as a "molecular evolutionary clock," it is well known that sequence change departs from a clock-like Poisson expectation. Through studying the deviations from a molecular clock, insight can be gained into the forces shaping evolution at the level of proteins. Generally, substitution patterns that show greater variance than the Poisson expectation a...

Competition has long been proposed as an important force in structuring mammalian communities. Although early work recognized that competition has a phylogenetic dimension, only with recent increases in the availability of phylogenies have true phylogenetic investigations of mammalian community structure become possible. We test whether the phylogenetic structure of 142 assemblages from three m...

The repeated presentation of an identical visual stimulus in the receptive field of a neuron may evoke different spiking patterns at each trial. Probabilistic methods are essential to understand the functional role of this variance within the neural activity. In that case, a Poisson process is the most common model of trial-to-trial variability. For a Poisson process, the variance of the spike ...

Tuberculosis is an infectious disease caused by Mycobacterium tuberculosis. Banyumas Regency one of the districts with quite high cases in Central Java. This study aims to analyze factors that affect number tuberculosis using regression analysis count data. Poisson simplest data model has assumption equidispersion, is, mean value equal variance. However, its application, these often not fulfill...

The phylogenetic structure of ecological communities can shed light on assembly processes, but the focus of phylogenetic structure research thus far has been on mature ecosystems. Here, I present the first investigation of phylogenetic community structure during succession. In a replicated chronosequence of 30 sites in northeastern Costa Rica, I found strong phylogenetic overdispersion at multi...