Readability Indices Structure and Optimal Features

The work considers formal structure and features of the readability indices widely employed in various information and education fields, including theory of communication, cognitive psychology, linguistics, and multiple applications. In spite of the importance and popularity of readability indices in practical research, their intrinsic properties have not yet been sufficiently investigated. This paper aims to fill this gap between the theory and application of these indices by presenting them in a uniform expression which permits analyzing their features and deriving new properties that are useful in practice. Three theorems are proved for relations between the units of a text structure. The general characteristics are illustrated by numerical examples which can be helpful for researchers and practitioners.