A note on an extreme left skewed unit distribution: Theory, modelling and data fitting

Abstract

In probability and statistics, unit distributions are used to model proportions, rates, and percentages, among other things. This paper is about a new one-parameter unit distribution, whose probability density function is defined by an original ratio of power and logarithmic functions. This function has a wide range of J shapes, some of which are more angular than others. In this sense, the proposed distribution can be thought of as an “extremely left skewed alternative” to the traditional power distribution. We discuss its main characteristics, including other features of the probability density function, some stochastic order results, the closed-form expression of the cumulative distribution function involving special integral functions, the quantile and hazard rate functions, simple expressions for the ordinary moments, skewness, kurtosis, moments generating function, incomplete moments, logarithmic moments and logarithmically weighted moments. Subsequently, a simple example of an application is given by the use of simulated data, with fair comparison to the power model supported by numerical and graphical illustrations. A new modelling strategy beyond the unit domain is also proposed and developed, with an application to a survival times data set.