  A reparametrized Dirichlet-multinomial distribution is introduced, and the
covariance matrix, as well as, the algorithm for calculating the PDF for n
species are provided. The distribution is suited for modelling the joint
distribution of pin-point cover data of spatially aggregated plant species, and
the parametrization ensures that the degree of spatially aggregation is
modelled by a parameter and the mean cover of the species is modelled by the
other parameters. This last property is convenient for using the distribution
in Bayesian hierarchical models where the mean cover of the different species
typically is modelled as latent variables.
