Bayesian modelling of skewness and kurtosis with two-piece scale and shape transformations

We introduce the family of univariate double two–piece distributions, obtained by using a density– based transformation of unimodal symmetric continuous distributions with a shape parameter. The resulting distributions contain five interpretable parameters that control the mode, as well as the scale and shape in each direction. Four-parameter subfamilies of this class of distributions that capture different types of asymmetry are presented. We propose interpretable scale and location-invariant benchmark priors and derive conditions for the existence of the corresponding posterior distribution. The prior structures used allow for meaningful comparisons through Bayes factors within flexible families of distributions. These distributions are applied to models in finance, internet traffic data, and medicine, comparing them with appropriate competitors.