Validity and Compatibility of Readability Formulas in Evaluating Persian Texts

In this research, the validity and compatibility of readability formulas in the evaluation of Persian texts were investigated. The main question was whether the results of evaluating Persian texts with readability formulas are valid. The research included three genres: textbooks, stories, and newspapers; and for each genre, three different texts were considered. For each text, three samples with at least one hundred words were selected by systematic random sampling. The samples were evaluated using Flesch-Kincaid, FOG and Fry readability formulas. The results of the research showed that the output of the formulas is stable in the textbook and newspaper genres, but it is instable in story texts that can be attributed to the variable language style of stories. In general, the results of this research and the reinterpretation of the results of the earlier studies showed that the output of readability formulas is not compatible with the structure of Persian language, and text evaluation of various genres suggests that applying readability formulas leads to evaluate Persian texts as "very difficult" or "invalid". It seems that in order to adapt these formulas, it is necessary to change the coefficients or add different indices that are compatible to the structural features of Persian language.