#### Readability Metrics

Readability metrics quantify text complexity using statistical measures of sentence structure and word characteristics. These formulas estimate the education level required to understand a text.

#### Available Metrics

##### Flesch Reading Ease (flesch)

Based on average sentence length and syllables per word.

- Formula: 206.835 - 1.015 × (words/sentences) - 84.6 × (syllables/words)
- Scale: 0-100 (higher scores = easier to read)

##### Flesch-Kincaid Grade Level (flesch_kincaid)

Converts readability to U.S. grade level equivalent.

- Formula: 0.39 × (words/sentences) + 11.8 × (syllables/words) - 15.59
- Output: U.S. grade level (e.g., 8.0 = 8th grade)

##### Gunning Fog Index (gunning_fog)

Estimates years of formal education needed. Uses complex words (3+ syllables).

- Formula: 0.4 × [(words/sentences) + 100 × (complex words/words)]
- Output: Years of education

##### SMOG Index (smog)

Simple Measure of Gobbledygook. Based on polysyllabic word count.

- Formula: 1.0430 × sqrt(polysyllables × 30/sentences) + 3.1291
- Output: Years of education
- Note: Requires minimum 30 sentences for reliable results

##### Automated Readability Index (ari)

Character-based formula (no syllable counting required).

- Formula: 4.71 × (characters/words) + 0.5 × (words/sentences) - 21.43
- Output: U.S. grade level

##### Coleman-Liau Index (coleman_liau)

Character-based formula using letters and sentences per 100 words.

- Formula: 0.0588 × L - 0.296 × S - 15.8
- Where: L = letters per 100 words, S = sentences per 100 words
- Output: U.S. grade level

#### Usage Notes

- Select metrics from the dropdown and optionally group by variables to compare documents
- Different formulas may produce slightly different grade level estimates
- These formulas measure surface-level text features (word length, sentence length)
- Short texts may produce less reliable scores

Learn More:

- quanteda textstat_readability Documentation