A Simple Tool for Choosing Dirichlet Priors

The Dirichlet distribution, also known as the multivariate beta distribution, is a probability distribution often employed to model the probabilities of a set of correlated, categorical outcomes/events. This is natural since the Dirichlet is a multivariate distribution with support on a probability simplex, where each dimension of the distribution is distributed univariate beta. In practical terms, this means that for each vector1 sampled from a Dirichlet, each and every value falls in the $(0,1)$ interval while the elements of the vector sum to one.