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The article presents the results of the analysis of the influence exerted by three lexical parameters (abstractness, frequency, and lexical diversity) on the complexity of educational texts. The representative corpus of academic texts, compiled for the study, comprises textbooks on social sciences for grades 5-11 (139971 tokens) and Biology (81712 tokens). The increasing complexity of the texts from grades 5-11 is confirmed by the steadily increasing Flash-Kincaid readability indices in both Social Science and Biology texts. The discrepancies between textbooks readability indices and the grade level are insignificant and do not exceed 1.0. Vocabulary Frequency as a text parameter does not correlate with complexity: the increasing complexity of texts across the grades is not accompanied by a stable increase in the corresponding frequency indices. The degree of abstractness of the texts increases in both lines of textbooks, however, texts on Social Studies have a higher degree of abstractness than Biology texts. The lexical diversity of texts in Biology textbooks is lower than the corresponding indicator in texts on social sciences, although the correlation of this parameter with text complexity requires extra studies. The results of the research and its algorithm can be used both in developing the theory of text complexity and in ranking academic texts for particular categories of readers.
Solnyshkina et al. (Wed,) studied this question.