Evaluating Two High Intermediate EFL and ESL Textbooks: A Comparative Study Based on Readability Indices

Readability is defined as the “comprehensibility of written text” [2,3]. It has been measured by various formulae developed for materials written for native speakers of a language (L1), or materials designed for second and/or foreign language students (L2). According to Brown et al. [4], being used with L1 texts, readability formulae provide a numerical index that estimates the reading difficulty of texts for native readers. Or, as Danielson [5] put it “A readability formula is usually a mathematical equation that strives to relate the comprehension of the reader and the linguistic characteristics of the text.”