The extended generalized lambda distribution system for fitting distributions to data: history, completion of theory, tables, applications, the “final word” on moment fits

Abstract

The generalized lambda distribution, GLD(λ1, λ2 λ3, λ4), is a four-parameter family that has been used for fitting distributions to a wide variety of data sets. The analysis of the λ3 and λ4 values that actually yield valid distributions has (until now) been incomplete. Moreover, because of computational problems and theoretical shortcomings, the moment space over which the GLD can be applied has been limited. This paper completes the analysis of the λ3 and λ4 values that are associated with valid distributions, improves previous computational methods to reduce errors associated with fitting data, expands the parameter space over which the GLD can be used, and uses a four-parameter generalized beta distribution to cover the portion of the parameter space where the GLD is not applicable. In short, the paper extends the GLD to an EGLD system that can be used for fitting distributions to data sets that that are cited in the literature as actually occurring in practice. Examples of use of the proposed system are included