Assessment of reading difficulty levels in Russian academic texts: Approaches and metrics

In this paper we explore to what extent text parameters, such as average number of words per sentence, syllables per word, nouns per sentence, frequency of content words, etc. can successfully rank Russian academic texts for different age and grade levels. We provide a brief overview of previous research on readability of Russian texts and describe the corpus of school textbooks on Social Studies (from 5-th to 11-th grade) compiled by the authors. We share our experience of using a variety of quantitative text complexity metrics and evaluate the measures of existing Russian text complexity formulas. Based on the tests of a set of extended text features, we propose one innovative metric for better prediction of Russian text complexity, i.e. the number of adjectives. As the results obtained compare favorably with the previously published results on the established complexity metrics for Russian texts, the study encourages the development of valid, reliable and transparent complexity tools for Russian texts.