For instance, an Automated Readability Index (ARI) has the following form for the document d: where c refers to the total number of letters in the document d, w is the total number of words and s denotes the total number of sentences in d. Since readability indexes rely on a few basic factors, precise assessment requires aggregation of many scores.
coh-Metrix-PORT tool (Aluisio et al., 2010) includes more than 50 different indexes for Portuguese language.