4. The Fog Index

4. The Fog Index

All misuse of language obscures the meaning of the communication (message). Several
methods have been devised to measure the readability of written language; the Fog Index
is one such. Readability is affected by:
„h The average length of the sentences, in words
„h The percentage of simple words
„h The percentage of verbs expressing forceful action
„h The proportion of familiar words
„h The proportion of abstract words
„h The proportion of personal references
„h The proportion of long words.
The Fog Index is based on the count of the number of words of 3 or more syllables in a
hundred-word sample of the passage being checked, as well as of the average sentence
length.
To determine the reading difficulty of a passage you will need to:
„h Select samples of 100 words each
„h Calculate the average number of words in the sentences of your sample by
counting the number of complete sentences and dividing that into the number
of words
„h Count the number of words of three or more syllables, excluding words with a
capital letter, compounds such as bookkeeper and words ending in ¡Ves or ¡Ved
„h Add the average number of words per sentence and the number of words of
three syllables or more, and multiply by 0.4.
This gives the Fog Index, which is graded as follows:
Index Reading Level
Less than 10 easy reading
11-12 the top 20% of 12-year-olds
13 the top 20% of 16-year-olds
14-16 first-year university student
17 university graduate.

This index can usefully be used in checking company communications, for example, to
ensure that they are comprehensible to the workers. A British Leyland memorandum to
workers, which concerned an ultimatum about productivity, reportedly had an index of
17: hardly likely to be effective in securing the workers‟ cooperation. Indeed, it is
claimed that the only management-to-worker communication which fell below an index
of 13 was a memo wishing all employees a Happy New Year!  British Leyland has in
the past notoriously suffered from poor industrial relations. Could ineffective
communication have been one of the causes?
Some recent American research found that:
Only 4 % of readers will understand a sentence of 27 words
But 75 % of readers will understand a sentence of 17 words
And 95 % of readers will understand a sentence of 8 words.