Adaptive Mixture of Student-t Distributions: The R Package AdMit

This introduction to the R package AdMit is a shorter version of Ardia et al. (2009), published in the Journal of Statistical Software. The package provides flexible functions to approximate a certain target distribution and to efficiently generate a sample of random draws from it, given only a kernel of the target density function. The core algorithm consists of the function AdMit which fits an adaptive mixture of Student-t distributions to the density of interest. Then, importance sampling or the independence chain MetropolisHastings algorithm is used to obtain quantities of interest for the target density, using the fitted mixture as the importance or candidate density. The estimation procedure is fully automatic and thus avoids the time-consuming and difficult task of tuning a sampling algorithm. The relevance of the package is shown in an example of a bivariate bimodal distribution.