Measuring Text Readability by Lexical Relations Retrieved from Wordnet

Current readability formulae have often been criticized for being unstable or not valid. They are mostly computed in regression analysis based on intuitively-chosen variables and graded readings. This study explores the relation between text readability and the conceptual categories proposed in Prototype Theory. These categories form a hierarchy: Basic level words like guitar represent the objects humans interact with most readily. They are acquired by children earlier than their superordinate words (or hypernyms) like stringed instrument and their subordinate words (or hyponyms) like acoustic guitar. Therefore, the readability of a text is presumably associated with the ratio of basic level words it contains. WordNet, a network of meaningfully related words, provides the best online open source database for studying such lexical relations. Our preliminary studies show that a basic level word can be identified by its frequency to form compounds (e.g. chair armchair) and the length difference from its hyponyms in average. We compared selected high school English textbook readings in terms of their basic level word ratios and their values calculated in several readability formulae. Basic level word ratios turned out to be the only one positively correlated with the text levels.