The folded exponential transformation for proportions

Summary. Several transformations have been suggested for proportions x. Most of these require that 0<x<1 and therefore fail when x=0 or x=1, which is quite common in practice. The paper proposes a transformation which allows x=0 and x=1. It is based on an extension of the exponential transformation and works well for moderately skewed unimodal distributions, whereas J-shaped or very skewed unimodel distributions are less well accommodated. Use of the transformation is exemplified with three data sets.