Gunning Fog Index

A traditional readability formula developed by Robert Gunning in 1952 that estimates the years of formal education a reader needs to understand a text on first reading. It is calculated from average sentence length plus the percentage of "complex" words — words with three or more syllables, excluding proper nouns, compounds, and common suffix forms. Like other shallow formulas (Flesch-Kincaid, SMOG), the Gunning Fog Index is easy to compute but is now known to correlate weakly with reader comprehension on realistic corpora; accessibility practitioners often pair it with other metrics or with NLP-based readability models.