LIXformule

LIXformule, commonly known as the LIX readability index, is a linguistic metric used to estimate how easy a text is to read. It is particularly associated with Swedish-language texts and has been used in education, publishing, and media to assess text complexity and to tailor content to target audiences.

The formula is LIX = W/S + (P/W) × 100, where W is the total number of words in the text, S is the number of sentences, and P is the number of long words. In this context, long words are typically defined as words longer than six letters. The first term, W/S, reflects average sentence length and thus syntactic complexity, while the second term, (P/W) × 100, represents the proportion of longer words and thus lexical difficulty.

Calculation steps are straightforward: count the words (W), count the sentences (S), identify long words (P), and apply the formula. The result is a single score used to compare texts or to monitor changes in readability over time.

LIX is used as a quick, language-based gauge of readability, especially in Swedish schools and media outlets. It provides a simple, interpretable benchmark but is not a comprehensive measure of understandability. It tends to favor longer texts and may be biased by word choice, genre, or stylistic conventions. Critics note that it omits syntax variety, cohesion, and reader background.

Example: a 200-word passage with 8 sentences and 40 long words yields W/S = 25 and (P/W) × 100 = 20, so LIX = 45.

See also: readability metrics, Flesch Reading Ease, SMOG.