For instance, a fog index of 12 requires the reading level of a United States high school senior (around 18 years old).
The test was developed in 1952 by Robert Gunning, an American businessman who had been involved in newspaper and textbook publishing.
[3] Additionally, the fog index is primarily applicable to English and may not accurately reflect readability in other languages.
Because the index was meant to measure clarity of expression within sentences, it assumed people saw each clause as a complete thought.
[8] For example, in Gibbon's The History of the Decline and Fall of the Roman Empire, the fog scores using the old and revised algorithms differ greatly.
A sample test using an automated Gunning Fog calculator on a random footnote from the text (#51: Dion, vol.